Inbred corn plant 90LDC2 and seeds thereof

ABSTRACT

According to the invention, there is provided an inbred corn plant designated 90LDC2. This invention thus relates to the plants, seeds and tissue cultures of the inbred corn plant 90LDC2, and to methods for producing a corn plant produced by crossing the inbred plant 90LDC2 with itself or with another corn plant, such as another inbred. This invention further relates to corn seeds and plants produced by crossing the inbred plant 90LDC2 with another corn plant, such as another inbred, and to crosses with related species. This invention further relates to the inbred and hybrid genetic complements of the inbred corn plant 90LDC2, and also to the RFLP and genetic isozyme typing profiles of inbred corn plant 90LDC2.

The present application claims the priority of co-pending U.S.Provisional Patent Application Ser. No. 60/073,342, filed Feb. 2, 1998,the entire disclosure of which is incorporated herein by referencewithout disclaimer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of corn breeding.In particular, the invention relates to inbred corn seed and plantsdesignated 90LDC2, and derivatives and tissue cultures of such inbredplants.

2. Description of Related Art

The goal of field crop breeding is to combine various desirable traitsin a single variety/hybrid. Such desirable traits include greater yield,better stalks, better roots, resistance to insecticides, herbicides,pests, and disease, tolerance to heat and drought, reduced time to cropmaturity, better agronomic quality, higher nutritional value, anduniformity in germination times, stand establishment, growth rate,maturity, and fruit size.

Breeding techniques take advantage of a plant's method of pollination.There are two general methods of pollination: a plant self-pollinates ifpollen from one flower is transferred to the same or another flower ofthe same plant. A plant cross-pollinates if pollen comes to it from aflower on a different plant.

Corn plants (Zea mays L.) can be bred by both self-pollination andcross-pollination. Both types of pollination involve the corn plant'sflowers. Corn has separate male and female flowers on the same plant,located on the tassel and the ear, respectively. Natural pollinationoccurs in corn when wind blows pollen from the tassels to the silks thatprotrude from the tops of the ear shoot.

Plants that have been self-pollinated and selected for type over manygenerations become homozygous at almost all gene loci and produce auniform population of true breeding progeny, a homozygous plant. A crossbetween two such homozygous plants produce a uniform population ofhybrid plants that are heterozygous for many gene loci. Conversely, across of two plants each heterozygous at a number of gene loci producesa population of hybrid plants that differ genetically and are notuniform. The resulting non-uniformity makes performance unpredictable.

The development of uniform corn plant hybrids requires the developmentof homozygous inbred plants, the crossing of these inbred plants, andthe evaluation of the crosses. Pedigree breeding and recurrent selectionare examples of breeding methods used to develop inbred plants frombreeding populations. Those breeding methods combine the geneticbackgrounds from two or more inbred plants or various other broad-basedsources into breeding pools from which new inbred plants are developedby selfing and selection of desired phenotypes. The new inbreds arecrossed with other inbred plants and the hybrids from these crosses areevaluated to determine which of those have commercial potential.

The pedigree breeding method involves crossing two genotypes. Eachgenotype can have one or more desirable characteristics lacking in theother; or, each genotype can complement the other. If the two originalparental genotypes do not provide all of the desired characteristics,other genotypes can be included in the breeding population. Superiorplants that are the products of these crosses are selfed and selected insuccessive generations. Each succeeding generation becomes morehomogeneous as a result of self-pollination and selection. Typically,this method of breeding involves five or more generations of selfing andselection: S₁ →S₂ ; S₂ →S₃ ; S₃ →S₄ ; S₄ →S₅, etc. After at least fivegenerations, the inbred plant is considered genetically pure.

Backcrossing can also be used to improve an inbred plant. Backcrossingtransfers a specific desirable trait from one inbred or non-inbredsource to an inbred that lacks that trait. This can be accomplished forexample by first crossing a superior inbred (A) (recurrent parent) to adonor inbred (non-recurrent parent), which carries the appropriate locusfor the trait in question. The progeny of this cross are then mated backto the superior recurrent parent (A) followed by selection in theresultant progeny for the desired trait to be transferred from thenon-recurrent parent. After five or more backcross generations withselection for the desired trait, the progeny are heterozygous for locicontrolling the characteristic being transferred, but are like thesuperior parent for most or almost all other genes. The last backcrossgeneration would be selfed to give pure breeding progeny for the locusor loci being transferred.

A single cross hybrid corn variety is the cross of two inbred plants,each of which has a genotype which complements the genotype of theother. The hybrid progeny of the first generation is designated F₁.Preferred F₁ hybrids are more vigorous than their inbred parents. Thishybrid vigor, or heterosis, is manifested in many polygenic traits,including markedly improved higher yields, better stalks, better roots,better uniformity and better insect and disease resistance. In thedevelopment of hybrids only the F₁ hybrid plants are sought. An F₁single cross hybrid is produced when two inbred plants are crossed. Adouble cross hybrid is produced from four inbred plants crossed in pairs(A×B and C×D) and then the two F₁ hybrids are crossed again (A×B)×(C×D).

The development of a hybrid corn variety involves three steps: (1) theselection of plants from various germplasm pools; (2) the selfing of theselected plants for several generations to produce a series of inbredplants, which, although different from each other, each breed true andare highly uniform; and (3) crossing the selected inbred plants withunrelated inbred plants to produce the hybrid progeny (F₁). During theinbreeding process in corn, the vigor of the plants decreases. Vigor isrestored when two unrelated inbred plants are crossed to produce thehybrid progeny (F₁). An important consequence of the homozygosity andhomogeneity of the inbred plants is that the hybrid between any twoinbreds is always the same. Once the inbreds that give a superior hybridhave been identified, hybrid seed can be reproduced indefinitely as longas the homogeneity of the inbred parents is maintained. Conversely, muchof the hybrid vigor exhibited by F₁ hybrids is lost in the nextgeneration (F₂). Consequently, seed from hybrid varieties is not usedfor planting stock. It is not generally beneficial for farmers to saveseed of F₁ hybrids. Rather, farmers purchase F₁ hybrid seed for plantingevery year.

North American farmers plant over 70 million acres of corn at thepresent time and there are extensive national and internationalcommercial corn breeding programs. A continuing goal of these cornbreeding programs is to develop high-yielding corn hybrids that arebased on stable inbred plants that maximize the amount of grain producedand minimize susceptibility to environmental stresses. To accomplishthis goal, the corn breeder must select and develop superior inbredparental plants for producing hybrids.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a corn plant designated90LDC2. Also provided are corn plants having all the physiological andmorphological characteristics of corn plant 90LDC2.

The inbred corn plant of the invention may further comprise, or have, acytoplasmic or nuclear factor that is capable of conferring malesterility. Parts of the corn plant of the present invention are alsoprovided, for example, pollen obtained from an inbred plant and an ovuleof the inbred plant.

The invention also concerns seed of the corn plant 90LDC2, which hasbeen deposited with the ATCC. The invention thus provides inbred cornseed designated 90LDC2, and having accession number PTA-305.

The inbred corn seed of the invention may be provided as an essentiallyhomogeneous population of inbred corn seed designated 90LDC2.Essentially homogeneous populations of inbred seed are those thatconsist essentially of the particular inbred seed, and are generallyfree from substantial numbers of other seed, so that the inbred seedforms between about 90% and about 100% of the total seed, andpreferably, between about 95% and about 100% of the total seed. Mostpreferably, an essentially homogeneous population of inbred corn seedwill contain between about 98.5%, 99%, 99.5% and about 99.9% of inbredseed, as measured by seed grow outs.

Therefore, in the practice of the present invention, hybrid seedgenerally forms at least about 97% of the total seed. However, even if apopulation of inbred corn seed was found, for some reason, to containabout 50%, or even about 20% or 15% of inbred seed, this would still bedistinguished from the small fraction of inbred seed that may be foundwithin a population of hybrid seed, e.g., within a bag of hybrid seed.In such a bag of hybrid seed offered for sale, the Governmentalregulations require that the hybrid seed be at least about 95% of thetotal seed. In the most preferred practice of the invention, the femaleinbred seed that may be found within a bag of hybrid seed will be about1% of the total seed, or less, and the male inbred seed that may befound within a bag of hybrid seed will be negligible, i.e., will be onthe order of about a maximum of 1 per 100,000, and usually less thanthis value.

The population of inbred corn seed of the invention is furtherparticularly defined as being essentially free from hybrid seed. Theinbred seed population may be separately grown to provide an essentiallyhomogeneous population of inbred corn plant designated 90LDC2.

In another aspect, the present invention provides for single locusconverted plants of 90LDC2. The single transferred locus may preferablybe a dominant or recessive allele. Preferably, the single transferredlocus will confer such traits as male sterility, herbicide resistance,insect resistance, resistance to bacterial, fungal, or viral disease,male fertility, enhanced nutritional quality, and industrial usage. Thesingle locus may be a naturally occurring maize gene or a transgeneintroduced through genetic engineering techniques.

In another aspect, the present invention provides a tissue culture ofregenerable cells of inbred corn plant 90LDC2. The tissue culture willpreferably be capable of regenerating plants having the physiologicaland morphological characteristics of the foregoing inbred corn plant,and of regenerating plants having substantially the same genotype as theforegoing inbred corn plant. Examples of some of the physiological andmorphological characteristics of the inbred corn plant 90LDC2 includecharacteristics related to yield, maturity, and kernel quality; each ofwhich are specifically disclosed herein. The regenerable cells in suchtissue cultures will preferably be embryos, meristematic cells, calli,pollen, leaves, anthers, roots, root tips, silk, flowers, kernels, ears,cobs, husks, or stalks, or protoplasts therefrom. Still further, thepresent invention provides corn plants regenerated from the tissuecultures of the invention, the plants having all the physiological andmorphological characteristics of corn plant 90LDC2.

In yet another aspect, the present invention provides processes forpreparing corn seed or plants, which processes generally comprisecrossing a first parent corn plant with a second parent corn plant,wherein at least one of the first or second parent corn plants is theinbred corn plant designated 90LDC2. These processes may be furtherexemplified as processes for preparing hybrid corn seed or plants,wherein a first inbred corn plant is crossed with a second, distinctinbred corn plant to provide a hybrid that has, as one of its parents,the inbred corn plant 90LDC2.

In a preferred embodiment, crossing comprises planting in pollinatingproximity seeds of a first and second parent corn plant, and preferably,seeds of a first inbred corn plant and a second, distinct inbred cornplant; cultivating or growing the seeds of said first and second parentcorn plants into plants that bear flowers; emasculating the male flowersof the first or second parent corn plant, (i.e., treating the flowers soas to prevent pollen production, in order to produce an emasculatedparent corn plant) allowing natural cross-pollination to occur betweenthe first and second parent corn plants; and harvesting the seeds fromthe emasculated parent corn plant. Where desired, the harvested seed isgrown to produce a corn plant or hybrid corn plant.

The present invention also provides corn seed and plants produced by aprocess that comprises crossing a first parent corn plant with a secondparent corn plant, wherein at least one of the first or second parentcorn plants is the inbred corn plant designated 90LDC2. In oneembodiment, corn plants produced by the process are first generation(F₁) hybrid corn plants produced by crossing an inbred in accordancewith the invention with another, distinct inbred. The present inventionfurther contemplates seed of an F₁ hybrid corn plant.

In certain exemplary embodiments, the invention provides an F₁ hybridcorn plant and seed thereof, which hybrid corn plant is designated5000010, having 90LDC2 as one inbred parent.

In yet a further aspect, the invention provides an inbred geneticcomplement of the corn plant designated 90LDC2. The phrase "geneticcomplement" is used to refer to the aggregate of nucleotide sequences,the expression of which sequences defines the phenotype of, in thepresent case, a corn plant, or a cell or tissue of that plant. An inbredgenetic complement thus represents the genetic make up of an inbredcell, tissue or plant, and a hybrid genetic complement represents thegenetic make up of a hybrid cell, tissue or plant. The invention thusprovides corn plant cells that have a genetic complement in accordancewith the inbred corn plant cells disclosed herein, and plants, seeds anddiploid plants containing such cells.

Plant genetic complements may be assessed by genetic marker profiles,and by the expression of phenotypic traits that are characteristic ofthe expression of the genetic complement, e.g., isozyme typing profiles.Thus, such corn plant cells may be defined as having an RFLP geneticmarker profile in accordance with the profile shown in Table 7, or agenetic isozyme typing profile in accordance with the profile shown inTable 8, or having both an RFLP genetic marker profile and a geneticisozyme typing profile in accordance with the profiles shown in Table 7and Table 8. It is understood that 90LDC2 could also be identified byother types of genetic markers such as, for example, Simple SequenceLength Polymorphisms (SSLPs) (Williams et al., 1990), Randomly AmplifiedPolymorphic DNAs (RAPDs), DNA Amplification Fingerprinting (DAF),Sequence Characterized Amplified Regions (SCARs), Arbitrary PrimedPolymerase Chain Reaction (AP-PCR), or Amplified Fragment LengthPolymorphisms (AFLPs) (EP 534 858, specifically incorporated herein byreference in its entirety).

In another aspect, the present invention provides hybrid geneticcomplements, as represented by corn plant cells, tissues, plants, andseeds, formed by the combination of a haploid genetic complement of aninbred corn plant of the invention with a haploid genetic complement ofa second corn plant, preferably, another, distinct inbred corn plant. Inanother aspect, the present invention provides a corn plant regeneratedfrom a tissue culture that comprises a hybrid genetic complement of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION I. DEFINITIONS OF PLANTCHARACTERISTICS

Barren Plants: Plants that are barren, i.e., lack an ear with grain, orhave an ear with only a few scattered kernels.

Cg: Colletotrichum graminicola rating. Rating times 10 is approximatelyequal to percent total plant infection.

CLN: Corn Lethal Necrosis (combination of Maize Chlorotic Mottle Virusand Maize Dwarf Mosaic virus) rating: numerical ratings are based on aseverity scale where 1=most resistant to 9=susceptible.

Cn: Corynebacterium nebraskense rating. Rating times 10 is approximatelyequal to percent total plant infection.

Cz: Cercospora zeae-maydis rating. Rating times 10 is approximatelyequal to percent total plant infection.

Dgg: Diatraea grandiosella girdling rating (values are percent plantsgirdled and stalk lodged).

Dropped Ears: Ears that have fallen from the plant to the ground.

Dsp: Diabrotica species root ratings (1=least affected to 9=severepruning).

Ear-Attitude: The attitude or position of the ear at harvest scored asupright, horizontal, or pendant.

Ear-Cob Color: The color of the cob, scored as white, pink, red, orbrown.

Ear-Cob Diameter: The average diameter of the cob measured at themidpoint.

Ear-Cob Strength: A measure of mechanical strength of the cobs tobreakage, scored as strong or weak.

Ear-Diameter: The average diameter of the ear at its midpoint.

Ear-Dry Husk Color: The color of the husks at harvest scored as buff,red, or purple.

Ear-Fresh Husk Color: The color of the husks 1 to 2 weeks afterpollination scored as green, red, or purple.

Ear-Husk Bract: The length of an average husk leaf scored as short,medium, or long.

Ear-Husk Cover: The average distance from the tip of the ear to the tipof the husks. Minimum value no less than zero.

Ear-Husk Opening: An evaluation of husk tightness at harvest scored astight, intermediate, or open.

Ear-Length: The average length of the ear.

Ear-Number Per Stalk: The average number of ears per plant.

Ear-Shank Internodes: The average number of internodes on the ear shank.

Ear-Shank Length: The average length of the ear shank.

Ear-Shelling Percent: The average of the shelled grain weight divided bythe sum of the shelled grain weight and cob weight for a single ear.

Ear-Silk Color: The color of the silk observed 2 to 3 days after silkemergence scored as green-yellow, yellow, pink, red, or purple.

Ear-Taper (Shape): The taper or shape of the ear scored as conical,semi-conical, or cylindrical.

Ear-Weight: The average weight of an ear.

Early Stand: The percent of plants that emerge from the ground asdetermined in the early spring.

ER: Ear rot rating (values approximate percent ear rotted).

Final Stand Count: The number of plants just prior to harvest.

GDUs: Growing degree units which are calculated by the Barger Method,where the heat units for a 24-h period are calculated as GDUs =[Maximumdaily temperature+Minimum daily temperature)/2]-50. The highest maximumdaily temperature used is 86° F. and the lowest minimum temperature usedis 50° F.

GDUs to Shed: The number of growing degree units (GDUs) or heat unitsrequired for an inbred line or hybrid to have approximately 50% of theplants shedding pollen as measured from time of planting. GDUs to shedis determined by summing the individual GDU daily values from plantingdate to the date of 50% pollen shed.

GDUs to Silk: The number of growing degree units for an inbred line orhybrid to have approximately 50% of the plants with silk emergence asmeasured from time of planting. GDUs to silk is determined by summingthe individual GDU daily values from planting date to the date of 50%silking.

Hc2: Helminthosporium carbonum race 2 rating. Rating times 10 isapproximately equal to percent total plant infection.

Hc3: Helminthosporium carbonum race 3 rating. Rating times 10 isapproximately equal to percent total plant infection.

Hm: Helminthosporium maydis race 0 rating. Rating times 10 isapproximately equal to percent total plant infection.

Ht1: Helminthosporium turcicum race 1 rating. Rating times 10 isapproximately equal to percent total plant infection.

Ht2: Helminthosporium turcicum race 2 rating. Rating times 10 isapproximately equal to percent total plant infection.

HtG: Chlorotic-lesion type resistance. +=indicates the presence of Htchlorotic-lesion type resistance; -=indicates absence of Htchlorotic-lesion type resistance; and +/-=indicates segregation of Htchlorotic-lesion type resistance. Rating times 10 is approximately equalto percent total plant infection.

Kernel-Aleurone Color: The color of the aleurone scored as white, pink,tan, brown, bronze, red, purple, pale purple, colorless, or variegated.

Kernel-Cap Color: The color of the kernel cap observed at dry stage,scored as white, lemon-yellow, yellow, or orange.

Kernel-Endosperm Color: The color of the endosperm scored as white, paleyellow, or yellow.

Kernel-Endosperm Type: The type of endosperm scored as normal, waxy, oropaque.

Kernel-Grade: The percent of kernels that are classified as rounds.

Kernel-Length: The average distance from the cap of the kernel to thepedicel.

Kernel-Number Per Row: The average number of kernels in a single row.

Kernel-Pericarp Color: The color of the pericarp scored as colorless,red-white crown, tan, bronze, brown, light red, cherry red, orvariegated.

Kernel-Row Direction: The direction of the kernel rows on the ear scoredas straight, slightly curved, spiral, or indistinct (scattered).

Kernel-Row Number: The average number of rows of kernels on a singleear.

Kernel-Side Color: The color of the kernel side observed at the drystage, scored as white, pale yellow, yellow, orange, red, or brown.

Kernel-Thickness: The distance across the narrow side of the kernel.

Kernel-Type: The type of kernel scored as dent, flint, or intermediate.

Kernel-Weight: The average weight of a predetermined number of kernels.

Kernel-Width: The distance across the flat side of the kernel.

Kz: Kabatiella zeae rating. Rating times 10 is approximately equal topercent total plant infection.

Leaf-Angle: Angle of the upper leaves to the stalk scored as upright (0to 30 degrees), intermediate (30 to 60 degrees), or lax (60 to 90degrees).

Leaf-Color: The color of the leaves 1 to 2 weeks after pollinationscored as light green, medium green, dark green, or very dark green.

Leaf-Length: The average length of the primary ear leaf.

Leaf-Longitudinal Creases: A rating of the number of longitudinalcreases on the leaf surface 1 to 2 weeks after pollination. Creases arescored as absent, few, or many.

Leaf-Marginal Waves: A rating of the waviness of the leaf margin 1 to 2weeks after pollination. Rated as none, few, or many.

Leaf-Number: The average number of leaves of a mature plant. Countingbegins with the cotyledonary leaf and ends with the flag leaf.

Leaf-Sheath Anthocyanin: A rating of the level of anthocyanin in theleaf sheath 1 to 2 weeks after pollination, scored as absent,basal-weak, basal-strong, weak or strong.

Leaf-Sheath Pubescence: A rating of the pubescence of the leaf sheath.Ratings are taken 1 to 2 weeks after pollination and scored as light,medium, or heavy.

Leaf-Width: The average width of the primary ear leaf measured at itswidest point.

LSS: Late season standability (values times 10 approximate percentplants lodged in disease evaluation plots).

Moisture: The moisture of the grain at harvest.

On1: Ostrinia nubilalis 1st brood rating (1=resistant to 9=susceptible).

On2: Ostrinia nubilalis 2nd brood rating (1=resistant to 9=susceptible).

Relative Maturity: A maturity rating based on regression analysis. Theregression analysis is developed by utilizing check hybrids and theirpreviously established day rating versus actual harvest moistures.Harvest moisture on the hybrid in question is determined and thatmoisture value is inserted into the regression equation to yield arelative maturity.

Root Lodging: Root lodging is the percentage of plants that root lodge.A plant is counted as root lodged if a portion of the plant leans fromthe vertical axis by approximately 30 degrees or more.

Seedling Color: Color of leaves at the 6 to 8 leaf stage.

Seedling Height: Plant height at the 6 to 8 leaf stage.

Seedling Vigor: A visual rating of the amount of vegetative growth on a1 to 9 scale, where 1 equals best. The score is taken when the averageentry in a trial is at the fifth leaf stage.

Selection Index: The selection index gives a single measure of hybrid'sworth based on information from multiple traits. One of the traits thatis almost always included is yield. Traits may be weighted according tothe level of importance assigned to them.

Sr: Sphacelotheca reiliana rating is actual percent infection.

Stalk-Anthocyanin: A rating of the amount of anthocyanin pigmentation inthe stalk. The stalk is rated 1 to 2 weeks after pollination as absent,basal-weak, basal-strong, weak, or strong.

Stalk-Brace Root Color: The color of the brace roots observed 1 to 2weeks after pollination as green, red, or purple.

Stalk-Diameter: The average diameter of the lowest visible internode ofthe stalk.

Stalk-Ear Height: The average height of the ear measured from the groundto the point of attachment of the ear shank of the top developed ear tothe stalk.

Stalk-Internode Direction: The direction of the stalk internode observedafter pollination as straight or zigzag.

Stalk-Internode Length: The average length of the internode above theprimary ear.

Stalk Lodging: The percentage of plants that did stalk lodge. Plants arecounted as stalk lodged if the plant is broken over or off below theear.

Stalk-Nodes With Brace Roots: The average number of nodes having braceroots per plant.

Stalk-Plant Height: The average height of the plant as measured from thesoil to the tip of the tassel.

Stalk-Tillers: The percent of plants that have tillers. A tiller isdefined as a secondary shoot that has developed as a tassel capable ofshedding pollen.

Staygreen: Staygreen is a measure of general plant health near the timeof black layer formation (physiological maturity). It is usuallyrecorded at the time the ear husks of most entries within a trial haveturned a mature color. Scoring is on a 1 to 9 basis where 1 equals best.

STR: Stalk rot rating (values represent severity rating of 1=25% ofinoculated internode rotted to 9=entire stalk rotted and collapsed).

SVC: Southeastern Virus Complex (combination of Maize Chlorotic DwarfVirus and Maize Dwarf Mosaic Virus) rating; numerical ratings are basedon a severity scale where 1=most resistant to 9=susceptible (1988reactions are largely Maize Dwarf Mosaic Virus reactions).

Tassel-Anther Color: The color of the anthers at 50% pollen shed scoredas green-yellow, yellow, pink, red, or purple.

Tassel-Attitude: The attitude of the tassel after pollination scored asopen or compact.

Tassel-Branch Angle: The angle of an average tassel branch to the mainstem of the tassel scored as upright (less than 30 degrees),intermediate (30 to 45 degrees), or lax (greater than 45 degrees).

Tassel-Branch Number: The average number of primary tassel branches.

Tassel-Glume Band: The closed anthocyanin band at the base of the glumescored as present or absent.

Tassel-Glume Color: The color of the glumes at 50% shed scored as green,red, or purple.

Tassel-Length: The length of the tassel measured from the base of thebottom tassel branch to the tassel tip.

Tassel-Peduncle Length: The average length of the tassel peduncle,measured from the base of the flag leaf to the base of the bottom tasselbranch.

Tassel-Pollen Shed: A visual rating of pollen shed determined by tappingthe tassel and observing the pollen flow of approximately five plantsper entry. Rated on a 1 to 9 scale where 9=sterile, 1=most pollen.

Tassel-Spike Length: The length of the spike measured from the base ofthe top tassel branch to the tassel tip.

Test Weight: Weight of the grain in pounds for a given volume (bushel)adjusted to 15.5% moisture.

Yield: Yield of grain at harvest adjusted to 15.5% moisture.

II. OTHER DEFINITIONS

Allele: Any of one or more alternative forms of a gene, all of whichalleles relate to one trait or characteristic. In a diploid cell ororganism, the two alleles of a given gene occupy corresponding loci on apair of homologous chromosomes.

Backcrossing: A process in which a breeder repeatedly crosses hybridprogeny back to one of the parents, for example, a first generationhybrid (F₁) with one of the parental genotypes of the F₁ hybrid.

Chromatography: A technique wherein a mixture of dissolved substancesare bound to a solid support followed by passing a column of fluidacross the solid support and varying the composition of the fluid. Thecomponents of the mixture are separated by selective elution.

Crossing: The mating of two parent plants.

Cross-pollination: Fertilization by the union of two gametes fromdifferent plants.

Diploid: A cell or organism having two sets of chromosomes.

Electrophoresis: A process by which particles suspended in a fluid aremoved under the action of an electrical field, and thereby separatedaccording to their charge and molecular weight. This method ofseparation is well known to those skilled in the art and is typicallyapplied to separating various forms of enzymes and of DNA fragmentsproduced by restriction endonucleases.

Emasculate: The removal of plant male sex organs or the inactivation ofthe organs with a cytoplasmic or nuclear factor conferring malesterility.

Enzymes: Molecules which can act as catalysts in biological reactions.

F₁ Hybrid: The first generation progeny of the cross of two plants.

Genetic Complement: An aggregate of nucleotide sequences, the expressionof which sequences defines the phenotype in corn plants, or componentsof plants including cells or tissue.

Genotype: The genetic constitution of a cell or organism.

Haploid: A cell or organism having one set of the two sets ofchromosomes in a diploid.

Isozymes: Detectable variants of an enzyme, the variants catalyzing thesame reaction(s) but differing from each other, e.g., in primarystructure and/or electrophoretic mobility. The differences betweenisozymes are under single locus, codominant control.

Consequently, electrophoretic separation to produce band patterns can beequated to different alleles at the DNA level. Structural differencesthat do not alter charge cannot be detected by this method.

Isozyme typing profile: A profile of band patterns of isozymes separatedby electrophoresis that can be equated to different alleles at the DNAlevel.

Linkage: A phenomenon wherein alleles on the same chromosome tend tosegregate together more often than expected by chance if theirtransmission was independent.

Marker: A readily detectable phenotype, preferably inherited incodominant fashion (both alleles at a locus in a diploid heterozygoteare readily detectable), with no environmental variance component, i.e.,heritability of 1.

90LDC2: The corn plant from which seeds having accession number PTA-305were obtained, as well as plants grown from those seeds.

Phenotype: The detectable characteristics of a cell or organism, whichcharacteristics are the manifestation of gene expression.

Quantitative Trait Loci (QTL): Genetic loci that contribute, at least inpart, certain numerically representable traits that are usuallycontinuously distributed.

Regeneration: The development of a plant from tissue culture.

RFLP genetic marker profile: A profile of band patterns of DNA fragmentlengths typically separated by agarose gel electrophoresis, afterrestriction endonuclease digestion of DNA.

Self-pollination: The transfer of pollen from the anther to the stigmaof the same plant.

Single Locus Converted (Conversion) Plant: Plants which are developed bya plant breeding technique called backcrossing wherein essentially allof the desired morphological and physiological characteristics of aninbred are recovered in addition to the single locus transferred intothe inbred via the backcrossing technique.

Tissue Culture: A composition comprising isolated cells of the same or adifferent type or a collection of such cells organized into parts of aplant.

Transgene: A genetic sequence which has been introduced into the genomeof a maize plant by transformation.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples that follow representtechniques discovered by the inventor to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments that are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

III. INBRED CORN PLANT 90LDC2

In accordance with one aspect of the present invention, there isprovided a novel inbred corn plant, designated 90LDC2. Inbred corn plant90LDC2 can be compared to inbred corn plants MM501D and 90LDC1, whichare proprietary inbreds of DEKALB Genetics Corporation, and LH210, aline developed by Holden's Foundation Seeds. 90LDC2 differssignificantly (at the 1%, 5%, or 10% level) from these inbred lines inseveral aspects (Table 1, Table 2 and Table 3).

                  TABLE 1                                                         ______________________________________                                        Comparison of 90LDC2 with LH210                                                       90LDC2   LH210    DIFF   #LOC  P VALUE                                ______________________________________                                        BARREN %                                                                              8.6      6.8      1.8    12    0.52                                     DROP % 1.2 0.7 0.5 12 0.66                                                    EHT INCH 33.0 39.0 -6.0 6 0.01*                                               FINAL 62.3 58.4 3.9 12 0.08+                                                  MST % 16.9 16.9 0.0 12 1.00                                                   PHT INCH 70.5 80.0 -9.5 6 0.00**                                              RTL % 10.0 6.3 3.7 11 0.12                                                    SHED GDU 1537.0 1635.5 -98.5 6 0.00**                                         SILK GDU 1573.3 1683.6 -110.3 6 0.00**                                        STL % 5.4 3.2 2.2 12 0.30                                                     YLD BU/A 33.0 24.9 8.1 12 0.16                                              ______________________________________                                         Signficance Levels are indicated as: + = 10%, * = 5%, ** = 1%.                Legend Abbreviations:                                                         BARREN % = Barren Plants (percent)                                            DROP % = Dropped Ears (percent)                                               EHT INCH = Ear Height (inches)                                                FINAL = Final Stand                                                           MST % = Moisture (percent)                                                    PHT INCH = Plant Height (inches)                                              RTL % = Root Lodging (percent)                                                SHED GDU = GDUs to Shed                                                       SILK GDU = GDUs to Silk                                                       STL % = Stalk Lodging (percent)                                               YLD BU/A = Yield (bushels/acre)                                          

                  TABLE 2                                                         ______________________________________                                        Comparison of 90LDC2 with MM501D                                                      90LDC2   MM501D   DIFF   #LOC  P VALUE                                ______________________________________                                        BARREN %                                                                              8.6      4.5      4.1    12    0.14                                     DROP % 1.2 0.8 0.4 12 0.76                                                    EHT INCH 33.0 23.2 9.8 6 0.00**                                               FINAL 62.3 61.9 0.4 12 0.85                                                   MST % 17.9 17.6 -0.7 12 0.57                                                  PHT INCH 70.5 61.7 8.8 6 0.00**                                               RTL % 10.0 0.4 9.6 12 0.00**                                                  SHED GDU 1537.0 1508.0 29.0 6 0.13                                            SILK GDU 1573.3 1545.3 28.0 6 0.16                                            STL % 5.4 4.0 1.3 12 0.52                                                     YLD BU/A 33.0 48.7 -15.7 12 0.00**                                          ______________________________________                                         Significance Levels are indicated as: + = 10%, * = 5%, ** = 1%.               Legend Abbreviations:                                                         BARREN % = Barren Plants (percent)                                            DROP % = Dropped Ears (percent)                                               EHT INCH = Ear Height (inches)                                                FINAL = Final Stand                                                           MST % = Moisture (percent)                                                    PHT INCH = Plant Height (inches)                                              RTL % = Root Lodging (percent)                                                SHED GDU = GDUs to Shed                                                       SILK GDU = GDUs to Silk                                                       STL % = Stalk Lodging (percent)                                               YLD BU/A = Yield (bushels/acre)                                          

                  TABLE 3                                                         ______________________________________                                        Comparison of 90LDC2 with 90LDC1                                                      90LDC2   90LDC1   DIFF   #LOC  P VALUE                                ______________________________________                                        BARREN %                                                                              5.9      5.0      0.9    20    0.73                                     DROP % 0.7 1.0 -0.3 20 0.67                                                   EHT INCH 32.2 26.0 6.2 13 0.00**                                              FINAL 56.0 60.7 -4.7 20 0.01*                                                 MST % 20.3 17.5 2.8 19 0.00**                                                 PHT INCH 69.5 68.0 1.5 13 0.53                                                RTL % 7.2 4.5 2.7 19 0.11                                                     SHED GDU 1566.0 1549.3 16.7 14 0.11                                           SILK GDU 1609.0 1623.4 -14.4 14 0.32                                          STL % 3.6 3.4 0.2 20 0.89                                                     YLD BU/A 37.8 53.3 -15.5 17 0.00**                                          ______________________________________                                         Significance Levels are indicated as: + = 10%, * = 5%, ** = 1%.               Legend Abbreviations:                                                         BARREN % = Barren Plants (percent)                                            DROP % = Dropped Ears (percent)                                               EHT INCH = Ear Height (inches)                                                FINAL = Final Stand                                                           MST % = Moisture (percent)                                                    PHT INCH = Plant Height (inches)                                              RTL % = Root Lodging (percent)                                                SHED GDU = GDUs to Shed                                                       SILK GDU = GDUs to Silk                                                       STL % = Stalk Lodging (percent)                                               YLD BU/A = Yield (bushels/acre)                                          

A. ORIGIN AND BREEDING HISTORY

Inbred plant 90LDC2 was derived from a cross between a line derived fromLH210 and the line MM501D. The origin and breeding history of inbredplant 90LDC2 can be summarized as follows:

Winter 1991-92 The inbred line MM501D (a proprietary DEKALB GeneticsCorporation inbred) was crossed with LH210 (a line developed by Holden'sFoundation Seeds) E117×E136

Spring 1992 S0 seed was grown. (Hawaii summer faster 9228).

Summer 1992 S1 seed was grown. (Hawaii summer faster 9228).

Winter 1992-93 S2 seed was grown ear to row (nursery rows F24:13-1,F25:1-56, F26:56-26). Key row: F25-08.

Summer 1993 S3 seed was grown ear to row (nursery rows 52:53-1,53:1-47). Key row: 52-32.

Summer 1994 S4 seed was grown ear to row (nursery rows 419:56-72,420:72-38). The seed from row 419-68 was named 90LDC2.

Winter 1994-95 S5 seed was grown ear to row (nursery row 6U:1340,6U:1355).

Summer 1995 S6 seed was grown ear to row (nursery rows 352:2-1,353:1-24).

Winter 1995-96 S7 seed was grown and increased (nursery rowsCC:20:67-43, 7E37:63-82, Fla 90-SS:201-220).

90LDC2 shows uniformity and stability within the limits of environmentalinfluence for the traits described hereinafter in Table 4. 90LDC2 hasbeen self-pollinated and ear-rowed a sufficient number of generationswith careful attention paid to uniformity of plant type to ensurehomozygosity and phenotypic stability. No variant traits have beenobserved or are expected in 90LDC2.

A deposit of 2500 seeds of the plant designated 90LDC2 has been madewith the American Type Culture Collection (ATCC), 10801 University Blvd.Manassas, Va. on Jun. 30, 1999. Those deposited seeds have been assignedaccession number PTA-305. The deposit was made in accordance with theterms and provisions of the Budapest Treaty relating to deposit ofmicroorganisms and is made for a term of at least thirty (30) years andat least five (05) years after the most recent request for thefurnishing of a sample of the deposit was received by the depository, orfor the effective term of the patent, whichever is longer, and will bereplaced if it becomes non-viable during that period.

Inbred corn plants can be reproduced by planting such inbred seeds,growing the resulting corn plants under self-pollinating orsib-pollinating conditions with adequate isolation using standardtechniques well known to an artisan skilled in the agricultural arts.Seeds can be harvested from such a plant using standard, well knownprocedures.

B. PHENOTYPIC DESCRIPTION

In accordance with another aspect of the present invention, there isprovided a corn plant having the physiological and morphologicalcharacteristics of corn plant 90LDC2. A description of the physiologicaland morphological characteristics of corn plant 90LDC2 is presented inTable 4.

                  TABLE 4                                                         ______________________________________                                        Morphological Traits for the 90LDC2 Phenotype                                              VALUE                                                            CHARACTERISTIC                                                                             90LDC2   L11210   MM501D 90LDC1                                  ______________________________________                                        1. STALK                                                                        Diameter (width) cm. 2.3 2.4 2.4 2.3                                          Anthocyanin Absent Strong Absent Absent                                       Nodes With Brace 1.9 2.2 2.1 2.1                                              Roots                                                                         Brace Root Color Absent Absent Absent Absent                                  Internode Direction Straight Straight Straight Straight                       Internode Length cm. 13.0 17.0 12.4 15.9                                      2. LEAF                                                                       Color Medium- Medium- --  Medium-                                              Green Green  Green                                                           Length cm. 78.3 81.0 72.0 79.8                                                Width cm. 8.8 9.0 10.2 9.8                                                    Sheath Anthocyanin Absent Weak Absent Absent                                  Sheath Pubescence Moderate -- Present Moderate                                Marginal Waves Few -- -- Few                                                  Longitudinal Creases Few Few -- Few                                           3. TASSEL                                                                     Attitude Open Open Compact Open                                               Length cm. 36.3 41.2 31.1 40.8                                                Spike Length cm. 19.5 24.6 19.4 19.3                                          Peduncle Length cm. 5.8 10.5 8.0 11.8                                         Branch Number 9.0 8.7 7.3 11.3                                                Anther Color Green- Pink Green- Green-                                         Yellow  Yellow Yellow                                                        Glume Color Green Green Green Green                                           Glume Band Absent Present Absent Absent                                       4. EAR                                                                        Silk Color Green- Red Green- Green-                                            Yellow  Yellow Yellow                                                        Number Per Stalk 1.5 1.1 1.0 1.1                                              Position (attitude) Pendant Upright Upright Pendant                           Length cm. 13.3 14.1 14.1 12.5                                                Shape Semi- Semi- Semi- Semi-                                                  Conical Conical Conical Conical                                              Diameter cm. 36.6 35.8 40.2 37.2                                              Weight gm. 86.3 79.7 111.1 90.8                                               Shank Length cm. 10.3 16.4 12.5 8.9                                           Husk Bract Short Short Short Short                                            Husk Cover cm. 7.6 11.9 2.9 8.4                                               Husk Opening -- Tight -- --                                                   Husk Color Fresh Green Green Green Green                                      Husk Color Dry Buff Buff Buff Buff                                            Cob Diameter cm. 24.0 18.0 23.0 18.2                                          Cob Color Red Red Red Red                                                     Shelling Percent 84.3 86.5 86.1 89.5                                          5. KERNEL                                                                     Row Number 15.4 12.9 14.2 14.6                                                Number Per Row 20.3 22.5 29.7 28.9                                            Row Direction Curved Curved Curved Curved                                     Type Dent Dent Dent Dent                                                      Cap Color -- Yellow Yellow --                                                 Side Color Orange Orange Orange Orange                                        Length (depth) mm. 10.5 11.0 10.8 10.7                                        Width mm. 8.5 7.9 8.3 7.5                                                     Thickness 5.2 4.8 4.2 3.8                                                     Weight of 1000K gm. 294.8 319.2 274.6 211.8                                   Endosperm Type Normal Normal Normal Normal                                    Endosperm Color Yellow Yellow Yellow Yellow                                 ______________________________________                                         *These are typical values. Values may vary due to environment. Other          values that are substantially equivalent are also within the scope of the     invention. Substantially equivalent refers to quantitative traits that        when compared do not show statistical differences of their means.        

IV. SINGLE LOCUS CONVERSIONS

When the term inbred corn plant is used in the context of the presentinvention, this also includes any single locus conversions of thatinbred. The term single locus converted plant as used herein refers tothose corn plants which are developed by a plant breeding techniquecalled backcrossing wherein essentially all of the desired morphologicaland physiological characteristics of an inbred are recovered in additionto the single locus transferred into the inbred via the backcrossingtechnique. Backcrossing methods can be used with the present inventionto improve or introduce a characteristic into the inbred. The termbackcrossing as used herein refers to the repeated crossing of a hybridprogeny back to one of the parental corn plants for that inbred. Theparental corn plant which contributes the locus or loci for the desiredcharacteristic is termed the nonrecurrent or donor parent. Thisterminology refers to the fact that the nonrecurrent parent is used onetime in the backcross protocol and therefore does not recur. Theparental corn plant to which the locus or loci from the nonrecurrentparent are transferred is known as the recurrent parent as it is usedfor several rounds in the backcrossing protocol (Poehlman et al., 1995;Fehr, 1987; Sprague and Dudley, 1988). In a typical backcross protocol,the original inbred of interest (recurrent parent) is crossed to asecond inbred (nonrecurrent parent) that carries the single locus ofinterest to be transferred. The resulting progeny from this cross arethen crossed again to the recurrent parent and the process is repeateduntil a corn plant is obtained wherein essentially all of the desiredmorphological and physiological characteristics of the recurrent parentare recovered in the converted plant, in addition to the singletransferred locus from the nonrecurrent parent. The backcross processmay be accelerated by the use of genetic markers, such as RFLP, SSLP,SNP or AFLP markers to identify plants with the greatest geneticcomplement from the recurrent parent.

The selection of a suitable recurrent parent is an important step for asuccessful backcrossing procedure. The goal of a backcross protocol isto alter or substitute a single trait or characteristic in the originalinbred. To accomplish this, a single locus of the recurrent inbred ismodified or substituted with the desired locus from the nonrecurrentparent, while retaining essentially all of the rest of the desiredgenetic, and therefore the desired physiological and morphologicalconstitution of the original inbred. The choice of the particularnonrecurrent parent will depend on the purpose of the backcross; one ofthe major purposes is to add some commercially desirable, agronomicallyimportant trait to the plant. The exact backcrossing protocol willdepend on the characteristic or trait being altered to determine anappropriate testing protocol. Although backcrossing methods aresimplified when the characteristic being transferred is a dominantallele, a recessive allele may also be transferred. In this instance itmay be necessary to introduce a test of the progeny to determine if thedesired characteristic has been successfully transferred.

Many single locus traits have been identified that are not regularlyselected for in the development of a new inbred but that can be improvedby backcrossing techniques. Single locus traits may or may not betransgenic; examples of these traits include, but are not limited to,male sterility, waxy starch, herbicide resistance, resistance forbacterial, fungal, or viral disease, insect resistance, male fertility,enhanced nutritional quality, industrial usage, yield stability, andyield enhancement. These genes are generally inherited through thenucleus, but may be inherited through the cytoplasm. Some knownexceptions to this are genes for male sterility, some of which areinherited cytoplasmically, but still act as single locus traits. Anumber of exemplary single locus traits are described in, for example,PCT Application WO 95/06128, the disclosure of which is specificallyincorporated herein by reference.

Examples of genes conferring male sterility include those disclosed inU.S. Pat. No. 3,861,709, U.S. Pat. No. 3,710,511, U.S. Pat. No.4,654,465, U.S. Pat. No. 5,625,132, and U.S. Pat. No. 4,727,219, each ofthe disclosures of which are specifically incorporated herein byreference in their entirety. A particularly useful type of malesterility gene is one which can be induced by exposure to a chemicalagent, for example, a herbicide (U.S. Pat. Ser. No. 08/927,368, filedSep. 11, 1997, the disclosure of which is specifically incorporatedherein by reference in its entirety). Both inducible and non-induciblemale sterility genes can increase the efficiency with which hybrids aremade, in that they eliminate the need to physically emasculate the cornplant used as a female in a given cross.

Where one desires to employ male-sterility systems with a corn plant inaccordance with the invention, it may be beneficial to also utilize oneor more male-fertility restorer genes. For example, where cytoplasmicmale sterility (CMS) is used, hybrid seed production requires threeinbred lines: (1) a cytoplasmically male-sterile line having a CMScytoplasm; (2) a fertile inbred with normal cytoplasm, which is isogenicwith the CMS line for nuclear genes ("maintainer line"); and (3) adistinct, fertile inbred with normal cytoplasm, carrying a fertilityrestoring gene ("restorer" line). The CMS line is propagated bypollination with the maintainer line, with all of the progeny being malesterile, as the CMS cytoplasm is derived from the female parent. Thesemale sterile plants can then be efficiently employed as the femaleparent in hybrid crosses with the restorer line, without the need forphysical emasculation of the male reproductive parts of the femaleparent.

The presence of a male-fertility restorer gene results in the productionof fully fertile F₁ hybrid progeny. If no restorer gene is present inthe male parent, male-sterile hybrids are obtained. Such hybrids areuseful where the vegetative tissue of the corn plant is utilized, e.g.,for silage, but in most cases, the seeds will be deemed the mostvaluable portion of the crop, so fertility of the hybrids in these cropsmust be restored. Therefore, one aspect of the current inventionconcerns the inbred corn plant 90LDC2 comprising a single locus capableof restoring male fertility in an otherwise male-sterile inbred orhybrid plant. Examples of male-sterility genes and correspondingrestorers which could be employed with the inbred of the invention arewell known to those of skill in the art of plant breeding and aredisclosed in, for instance, U.S. Pat. No. 5,530,191; U.S. Pat. No.5,689,041; U.S. Pat. No. 5,741,684; and U.S. Pat. No. 5,684,242, thedisclosures of which are each specifically incorporated herein byreference in their entirety.

Direct selection may be applied where the single locus acts as adominant trait. An example of a dominant trait is the herbicideresistance trait. For this selection process, the progeny of the initialcross are sprayed with the herbicide prior to the backcrossing. Thespraying eliminates any plants which do not have the desired herbicideresistance characteristic, and only those plants which have theherbicide resistance gene are used in the subsequent backcross. Thisprocess is then repeated for all additional backcross generations.

Many useful single locus traits are those which are introduced bygenetic transformation techniques. Methods for the genetictransformation of maize are known to those of skill in the art. Forexample, methods which have been described for the genetictransformation of maize include electroporation (U.S. Pat. No.5,384,253), electrotransformation (U.S. Pat. No. 5,371,003),microprojectile bombardment (U.S. Pat. No. 5,550,318; U.S. Pat. No.5,736,369, U.S. Pat. No. 5,538,880; and PCT Publication WO 95/06128),Agrobacterium-mediated transformation (U.S. Pat. No. 5,591,616 and E.P.Publication EP672752), direct DNA uptake transformation of protoplasts(Omirulleh et al., 1993) and silicon carbide fiber-mediatedtransformation (U.S. Pat. No. 5,302,532 and U.S. Pat. No. 5,464,765).

A type of single locus trait which can be introduced by genetictransformation (U.S. Pat. No. 5,554,798) and has particular utility is agene which confers resistance to the herbicide glyphosate. Glyphosateinhibits the action of the enzyme EPSPS, which is active in thebiosynthetic pathway of aromatic amino acids. Inhibition of this enzymeleads to starvation for the amino acids phenylalanine, tyrosine, andtryptophan and secondary metabolites derived therefrom. Mutants of thisenzyme are available which are resistant to glyphosate. For example,U.S. Pat. No. 4,535,060 describes the isolation of EPSPS mutations whichconfer glyphosate resistance upon organisms having the Salmonellatyphimurium gene for EPSPS, aroA. A mutant EPSPS gene having similarmutations has also been cloned from Zea mays. The mutant gene encodes aprotein with amino acid changes at residues 102 and 106 (PCT PublicationWO 97/04103). When a plant comprises such a gene, a herbicide resistantphenotype results.

Plants having inherited a transgene comprising a mutated EPSPS gene may,therefore, be directly treated with the herbicide glyphosate without theresult of significant damage to the plant. This phenotype providesfarmers with the benefit of controlling weed growth in a field of plantshaving the herbicide resistance trait by application of the broadspectrum herbicide glyphosate. For example, one could apply theherbicide ROUNDUP™, a commercial formulation of glyphosate manufacturedand sold by the Monsanto Company, over the top in fields whereglyphosate resistant corn plants are grown. The herbicide applicationrates may typically range from 4 ounces of ROUNDUP™ to 256 ouncesROUNDUP™ per acre. More preferably, about 16 ounces to about 64 ouncesper acre of ROUNDUP™ may be applied to the field. However, theapplication rate may be increased or decreased as needed, based on theabundance and/or type of weeds being treated. Additionally, depending onthe location of the field and weather conditions, which will influenceweed growth and the type of weed infestation, it may be desirable toconduct further glyphosate treatments. The second glyphosate applicationwill also typically comprise an application rate of about 16 ounces toabout 64 ounces of ROUNDUP™ per acre treated. Again, the treatment ratemay be adjusted based on field conditions. Such methods of applicationof herbicides to agricultural crops are well known in the art and aresummarized in general in Anderson (1983).

Alternatively, more than one single locus trait may be introgressed intoan elite inbred by the method of backcross conversion. A selectablemarker gene and a gene encoding a protein which confers a trait ofinterest may be simultaneously introduced into a maize plant as a resultof genetic transformation. Usually one or more introduced genes willintegrate into a single chromosome site in the host cell's genome. Forexample, a selectable marker gene encoding phosphinothricin acetyltransferase (PPT) (e.g., a bar gene) and conferring resistance to theactive ingredient in some herbicides by inhibiting glutamine synthetase,and a gene encoding an endotoxin from Bacillus thuringiensis (Bt) andconferring resistance to particular classes of insects, e.g.,lepidopteran insects, in particular the European Corn Borer, may besimultaneously introduced into a host genome. Furthermore, through theprocess of backcross conversion more than one transgenic trait may betransferred into an elite inbred.

The waxy characteristic is an example of a recessive trait. In thisexample, the progeny resulting from the first backcross generation (BC1)must be grown and selfed. A test is then run on the selfed seed from theBC1 plant to determine which BC1 plants carried the recessive gene forthe waxy trait. In other recessive traits additional progeny testing,for example growing additional generations such as the BC1S1, may berequired to determine which plants carry the recessive gene.

V. ORIGIN AND BREEDING HISTORY OF AN EXEMPLARY SINGLE LOCUS CONVERTEDPLANT

85DSD1 MLms is a single locus conversion of 85DGD1 to cytoplasmic malesterility. 85DGD1 MLms was derived using backcross methods. 85DGD1 (aproprietary inbred of DEKALB Genetics Corporation) was used as therecurrent parent and MLms, a germplasm source carrying ML cytoplasmicsterility, was used as the nonrecurrent parent. The breeding history ofthe single locus converted inbred 85DGD1 MLms can be summarized asfollows:

Hawaii Nurseries Planting Date 04-02-1992 Made up S-O: Female row 585male row 500

Hawaii Nurseries Planting Date 07-15-1992 S-O was grown and plants werebackcrossed times 85DGD1 (rows 444' 443)

Hawaii Nurseries Planting Date 11-18-1992 Bulked seed of the BC1 wasgrown and backcrossed times 85DGD1 (rows V3-27' V3-26)

Hawaii Nurseries Planting Date 04-02-1993 Bulked seed of the BC2 wasgrown and backcrossed times 85DGD1 (rows 37' 36)

Hawaii Nurseries Planting Date 07-14-1993 Bulked seed of the BC3 wasgrown and backcrossed times 85DGD1 (rows 99' 98)

Hawaii Nurseries Planting Date 10-28-1993 Bulked seed of BC4 was grownand backcrossed times 85DGD1 (rows KS-63' KS-62)

Summer 1994 A single ear of the BC5 was grown and backcrossed times85DGD1 (MC94-822' MC94-822-7)

Winter 1994 Bulked seed of the BC6 was grown and backcrossed times85DGD1 (3Q-1' 3Q-2)

Summer 1995 Seed of the BC7 was bulked and named 85DGD1 MLms.

VI. TISSUE CULTURE AND IN VITRO REGENERATION OF CORN PLANTS

A further aspect of the invention relates to tissue culture of cornplants designated 90LDC2. As used herein, the term "tissue culture"indicates a composition comprising isolated cells of the same or adifferent type or a collection of such cells organized into parts of aplant. Exemplary types of tissue cultures are protoplasts, calli andplant cells that are intact in plants or parts of plants, such asembryos, pollen, flowers, kernels, ears, cobs, leaves, husks, stalks,roots, root tips, anthers, silk, and the like. In a preferredembodiment, the tissue culture is embryos, protoplasts, meristematiccells, pollen, leaves or anthers. Means for preparing and maintainingplant tissue cultures are well known in the art (U.S. Pat. No.5,554,798; and U.S. Pat. No. 5,550,318, each incorporated herein byreference in their entirety). By way of example, a tissue culturecomprising organs such as tassels or anthers has been used to produceregenerated plants (U.S. patent application Ser. No. 07/992,637, filedDec. 18, 1992; and U.S. Pat. No. 5,322,789; the disclosures of which areincorporated herein by reference).

VII. TASSEL/ANTHER CULTURE

Tassels contain anthers which in turn enclose microspores. Microsporesdevelop into pollen. For anther/microspore culture, if tassels are theplant composition, they are preferably selected at a stage when themicrospores are uninucleate, that is, include only one, rather than 2 or3 nuclei. Methods to determine the correct stage are well known to thoseskilled in the art and include mitramycin fluorescent staining (Pace etat, 1987), trypan blue (preferred) and acetocarmine squashing. Themid-uninucleate microspore stage has been found to be the developmentalstage most responsive to the subsequent methods disclosed to ultimatelyproduce plants.

Although microspore-containing plant organs such as tassels cangenerally be pretreated at any cold temperature below about 25° C., arange of 4 to 25° C. is preferred, and a range of 8 to 14° C. isparticularly preferred. Although other temperatures yield embryoids andregenerated plants, cold temperatures produce optimum response ratescompared to pretreatment at temperatures outside the preferred range.Response rate is measured as either the number of embryoids or thenumber of regenerated plants per number of microspores initiated inculture. Exemplary methods of microspore culture are disclosed in, forexample, U.S. Pat. No. 5,322,789 and U.S. Pat. No. 5,445,961, thedisclosures of which are specifically incorporated herein by reference.

Although not required, when tassels are employed as the plant organ, itis generally preferred to sterilize their surface. Following surfacesterilization of the tassels, for example, with a solution of calciumhypochloride, the anthers are removed from about 70 to 150 spikelets(small portions of the tassels) and placed in a preculture orpretreatment medium. Larger or smaller amounts can be used depending onthe number of anthers.

When one elects to employ tassels directly, tassels are preferablypretreated at a cold temperature for a predefined time, preferably at10° C. for about 4 days. After pretreatment of a whole tassel at a coldtemperature, dissected anthers are further pretreated in an environmentthat diverts microspores from their developmental pathway. The functionof the preculture medium is to switch the developmental program from oneof pollen development to that of embryoid/callus development. Anembodiment of such an environment in the form of a preculture mediumincludes a sugar alcohol, for example mannitol or sorbitol, inositol orthe like. An exemplary synergistic combination is the use of mannitol ata temperature of about 10° C. for a period ranging from about 10 to 14days. In a preferred embodiment, 3 ml of 0.3 M mannitol combined with 50mg/l of ascorbic acid, silver nitrate, and colchicine is used forincubation of anthers at 10° C. for between 10 and 14 days. Anotherembodiment is to substitute sorbitol for mannitol. The colchicineproduces chromosome doubling at this early stage. The chromosomedoubling agent is preferably only present at the preculture stage.

It is believed that the mannitol or other similar carbon structure orenvironmental stress induces starvation and functions to forcemicrospores to focus their energies on entering developmental stages.The cells are unable to use, for example, mannitol as a carbon source atthis stage. It is believed that these treatments confuse the cellscausing them to develop as embryoids and plants from microspores.Dramatic increases in development from these haploid cells, as high as25 embryoids in 10⁴ microspores, have resulted from using these methods.

In embodiments where microspores are obtained from anthers, microsporescan be released from the anthers into an isolation medium following themannitol preculture step. One method of release is by disruption of theanthers, for example, by chopping the anthers into pieces with a sharpinstrument, such as a razor blade, scalpel, or Waring blender. Theresulting mixture of released microspores, anther fragments, andisolation medium are then passed through a filter to separatemicrospores from anther wall fragments. An embodiment of a filter is amesh, more specifically, a nylon mesh of about 112 mm pore size. Thefiltrate which results from filtering the microspore-containing solutionis preferably relatively free of anther fragments, cell walls, and otherdebris.

In a preferred embodiment, isolation of microspores is accomplished at atemperature below about 25° C. and, preferably at a temperature of lessthan about 15° C. Preferably, the isolation media, dispersing tool(e.g., razor blade), funnels, centrifuge tubes, and dispersing container(e.g., petri dish) are all maintained at the reduced temperature duringisolation. The use of a precooled dispersing tool to isolate maizemicrospores has been reported (Gaillard et al., 1991).

Where appropriate and desired, the anther filtrate is then washedseveral times in isolation medium. The purpose of the washing andcentrifugation is to eliminate any toxic compounds which are containedin the non-microspore part of the filtrate and are created by thechopping process. The centrifugation is usually done at decreasing spinspeeds, for example, 1000, 750, and finally 500 rpms. The result of theforegoing steps is the preparation of a relatively pure tissue culturesuspension of microspores that are relatively free of debris and antherremnants.

To isolate microspores, an isolation media is preferred. An isolationmedia is used to separate microspores from the anther walls whilemaintaining their viability and embryogenic potential. An illustrativeembodiment of an isolation media includes a 6% sucrose or maltosesolution combined with an antioxidant such as 50 mg/l of ascorbic acid,0.1 mg/l biotin, and 400 mg/l of proline, combined with 10 mg/l ofnicotinic acid and 0.5 mg/l AgNO₃. In another embodiment, the biotin andproline are omitted.

An isolation media preferably has a higher antioxidant level where usedto isolate microspores from a donor plant (a plant from which a plantcomposition containing a microspore is obtained) that is field grown incontrast to greenhouse grown. A preferred level of ascorbic acid in anisolation medium is from about 50 mg/l to about 125 mg/l and, morepreferably from about 50 mg/l to about 100 mg/l.

One can find particular benefit in employing a support for themicrospores during culturing and subculturing. Any support thatmaintains the cells near the surface can be used. The microsporesuspension is layered onto a support, for example by pipetting. Thereare several types of supports which are suitable and are within thescope of the invention. An illustrative embodiment of a solid support isa TRANSWELL® culture dish. Another embodiment of a solid support fordevelopment of the microspores is a bilayer plate wherein liquid mediais on top of a solid base. Other embodiments include a mesh or amillipore filter. Preferably, a solid support is a nylon mesh in theshape of a raft. A raft is defined as an approximately circular supportmaterial which is capable of floating slightly above the bottom of atissue culture vessel, for example, a petri dish, of about a 60 or 100mm size, although any other laboratory tissue culture vessel willsuffice. In an illustrative embodiment, a raft is about 55 mm indiameter.

Culturing isolated microspores on a solid support, for example, on a 10mm pore nylon raft floating on 2.2 ml of medium in a 60 mm petri dish,prevents microspores from sinking into the liquid medium and thusavoiding low oxygen tension. These types of cell supports enable theserial transfer of the nylon raft with its associatedmicrospore/embryoids ultimately to full strength medium containingactivated charcoal and solidified with, for example, GELRITE™(solidifying agent). The charcoal is believed to absorb toxic wastes andintermediaries. The solid medium allows embryoids to mature.

The liquid medium passes through the mesh while the microspores areretained and supported at the medium-air interface. The surface tensionof the liquid medium in the petri dish causes the raft to float. Theliquid is able to pass through the mesh; consequently, the microsporesstay on top. The mesh remains on top of the total volume of liquidmedium. An advantage of the raft is to permit diffusion of nutrients tothe microspores. Use of a raft also permits transfer of the microsporesfrom dish to dish during subsequent subculture with minimal loss,disruption, or disturbance of the induced embryoids that are developing.The rafts represent an advantage over the multi-welled TRANSWELL®plates, which are commercially available from COSTAR, in that thecommercial plates are expensive. Another disadvantage of these plates isthat to achieve the serial transfer of microspores to subsequent media,the membrane support with cells must be peeled off the insert in thewells. This procedure does not produce as good a yield nor as efficienttransfers, as when a mesh is used as a vehicle for cell transfer.

The culture vessels can be further defined as either (1) a bilayer 60 mmpetri plate wherein the bottom 2 ml of medium are solidified with 0.7%agarose overlaid with 1 mm of liquid containing the microspores; (2) anylon mesh raft wherein a wafer of nylon is floated on 1.2 ml of mediumand 1 ml of isolated microspores is pipetted on top; or (3) TRANSWELL®plates wherein isolated microspores are pipetted onto membrane insertswhich support the microspores at the surface of 2 ml of medium.

After the microspores have been isolated, they are cultured in a lowstrength anther culture medium until about the 50 cell stage when theyare subcultured onto an embryoid/callus maturation medium. Medium isdefined at this stage as any combination of nutrients that permit themicrospores to develop into embryoids or callus. Many examples ofsuitable embryoid/callus promoting media are well known to those skilledin the art. These media will typically comprise mineral salts, a carbonsource, vitamins, growth regulations. A solidifying agent is optional. Apreferred embodiment of such a media is referred to by the inventor asthe "D medium" which typically includes 6N1 salts, AgNO₃ and sucrose ormaltose.

In an illustrative embodiment, 1 ml of isolated microspores are pipettedonto a 10 mm nylon raft and the raft is floated on 1.2 ml of medium "D,"containing sucrose or preferably maltose. Both calli and embryoids candevelop. Calli are undifferentiated aggregates of cells. Type I is arelatively compact, organized, and slow growing callus. Type II is asoft, friable, and fast-growing one. Embryoids are aggregates exhibitingsome embryo-like structures. The embryoids are preferred for subsequentsteps to regenerating plants. Culture medium "D" is an embodiment ofmedium that follows the isolation medium and replaces it. Medium "D"promotes growth to an embryoid/callus. This medium comprises 6N1 saltsat 1/8 the strength of a basic stock solution (major components) andminor components, plus 12% sucrose, or preferably 12% maltose, 0.1 mg/lB1, 0.5 mg/l nicotinic acid, 400 mg/l proline and 0.5 mg/l silvernitrate. Silver nitrate is believed to act as an inhibitor to the actionof ethylene. Multi-cellular structures of approximately 50 cells eachgenerally arise during a period of 12 days to 3 weeks. Serial transferafter a two week incubation period is preferred.

After the petri dish has been incubated for an appropriate period oftime, preferably two weeks in the dark at a predefined temperature, araft bearing the dividing microspores is transferred serially to solidbased media which promote embryo maturation. In an illustrativeembodiment, the incubation temperature is 30° C. and the mesh raftsupporting the embryoids is transferred to a 100 mm petri dishcontaining the 6N1-TGR-4P medium, an "anther culture medium." Thismedium contains 6N1 salts, supplemented with 0.1 mg/l TIBA, 12% sugar(sucrose, maltose, or a combination thereof), 0.5% activated charcoal,400 mg/l proline, 0.5 mg/l B, 0.5 mg/l nicotinic acid, and 0.2 percentGELRITE™ (solidifying agent) and is capable of promoting the maturationof the embryoids. Higher quality embryoids, that is, embryoids whichexhibit more organized development, such as better shoot meristemformation without precocious germination, were typically obtained withthe transfer to full strength medium compared to those resulting fromcontinuous culture using only, for example, the isolated microsporeculture (IMC) Medium "D." The maturation process permits the pollenembryoids to develop further in route toward the eventual regenerationof plants. Serial transfer occurs to fill strength solidified 6N1 mediumusing either the nylon raft, the TRANSWELL® membrane, or bilayer plates,each one requiring the movement of developing embryoids to permit afterdevelopment into physiologically more mature structures. In anespecially preferred embodiment, microspores are isolated in anisolation media comprising about 6% maltose, cultured for about twoweeks in an embryoid/calli induction medium comprising about 12% maltoseand then transferred to a solid medium comprising about 12% sucrose.

At the point of transfer of the raft, after about two weeks ofincubation, embryoids exist on a nylon support. The purpose oftransferring the raft with the embryoids to a solidified medium afterthe incubation is to facilitate embryo maturation. Mature embryoids atthis point are selected by visual inspection indicated by zygoticembryo-like dimensions and structures and are transferred to the shootinitiation medium. It is preferred that shoots develop before roots, orthat shoots and roots develop concurrently. If roots develop beforeshoots, plant regeneration can be impaired. To produce solidified media,the bottom of a petri dish of approximately 100 mm is covered with about30 ml of 0.2% GELRITE™ solidified medium. A sequence of regenerationmedia are used for whole plant formation from the embryoids.

During the regeneration process, individual embryoids are induced toform plantlets. The number of different media in the sequence can varydepending on the specific protocol used. Finally, a rooting medium isused as a prelude to transplanting to soil. When plantlets reach aheight of about 5 cm, they are then transferred to pots for furthergrowth into flowering plants in a greenhouse by methods well known tothose skilled in the art.

Plants have been produced from isolated microspore cultures by themethods disclosed herein, including self-pollinated plants. The rate ofembryoid induction was much higher with the synergistic preculturetreatment consisting of a combination of stress factors, including acarbon source which can be capable of inducing starvation, a coldtemperature, and colchicine, than has previously been reported. Anillustrative embodiment of the synergistic combination of treatmentsleading to the dramatically improved response rate compared to priormethods, is a temperature of about 10° C., mannitol as a carbon source,and 0.05% colchicine.

The inclusion of ascorbic acid, an anti-oxidant, in the isolation mediumis preferred for maintaining good microspore viability. However, thereseems to be no advantage to including mineral salts in the isolationmedium. The osmotic potential of the isolation medium was maintainedoptimally with about 6% sucrose, although a range of 2% to 12% is withinthe scope of this invention.

In an embodiment of the embryoid/callus organizing media, mineral saltsconcentration in IMC Culture Media "D" is (1/8×), the concentrationwhich is used also in anther culture medium. The 6N1 salts majorcomponents have been modified to remove ammonium nitrogen. Osmoticpotential in the culture medium is maintained with about 12% sucrose andabout 400 mg/l proline. Silver nitrate (0.5 mg/l) was included in themedium to modify ethylene activity. The preculture media is furthercharacterized by having a pH of about 5.7 to 6.0. Silver nitrate andvitamins do not appear to be crucial to this medium but do improve theefficiency of the response.

Whole anther cultures can also be used in the production ofmonocotyledonous plants from a plant culture system. There are somebasic similarities of anther culture methods and microspore culturemethods with regard to the media used. A difference from isolatedmicrospore cultures is that undisrupted anthers are cultured, so that asupport, e.g., a nylon mesh support, is not needed. The first step indeveloping the anther cultures is to incubate tassels at a coldtemperature. A cold temperature is defined as less than about 25° C.More specifically, the incubation of the tassels is preferably performedat about 10° C. A range of 8 to 14° C. is also within the scope of theinvention. The anthers are then dissected from the tassels, preferablyafter surface sterilization using forceps, and placed on solidifiedmedium. An example of such a medium is designated by the inventors as 6N1-TGR-P4.

The anthers are then treated with environmental conditions that arecombinations of stresses that are capable of diverting microspores fromgametogenesis to embryogenesis. It is believed that the stress effect ofsugar alcohols in the preculture medium, for example, mannitol, isproduced by inducing starvation at the predefined temperature. In oneembodiment, the incubation pretreatment is for about 14 days at 10° C.It was found that treating the anthers in addition with a carbonstructure, an illustrative embodiment being a sugar alcohol, preferablymannitol, produces dramatically higher anther culture response rates asmeasured by the number of eventually regenerated plants, than bytreatment with either cold treatment or mannitol alone. These resultsare particularly surprising in light of teachings that cold is betterthan mannitol for these purposes, and that warmer temperatures interactwith mannitol better.

To incubate the anthers, they are floated on a preculture medium whichdiverts the microspores from gametogenesis, preferably on a mannitolcarbon structure, more specifically, 0.3 M of mannitol plus 50 mg/l ofascorbic acid. Three milliliters is about the total amount in a dish,for example, a tissue culture dish, more specifically, a 60 mm petridish. Anthers are isolated from about 120 spikelets for one dish yieldsabout 360 anthers.

Chromosome doubling agents can be used in the preculture media foranther cultures. Several techniques for doubling chromosome number(Jensen, 1974; Wan et al., 1989) have been described. Colchicine is oneof the doubling agents. However, developmental abnormalities arisingfrom in vitro cloning are further enhanced by colchicine treatments, andprevious reports indicated that colchicine is toxic to microspores. Theaddition of colchicine in increasing concentrations during mannitolpretreatment prior to anther culture and microspore culture has achievedimproved percentages.

An illustrative embodiment of the combination of a chromosome doublingagent and preculture medium is one which contains colchicine. In aspecific embodiment, the colchicine level is preferably about 0.05%. Theanthers remain in the mannitol preculture medium with the additives forabout 10 days at 10° C. Anthers are then placed on maturation media, forexample, that designated 6N1-TGR-P4, for 3 to 6 weeks to induceembryoids. If the plants are to be regenerated from the embryoids, shootregeneration medium is employed, as in the isolated microspore proceduredescribed in the previous sections. Other regeneration media can be usedsequentially to complete regeneration of whole plants.

The anthers are then exposed to embryoid/callus promoting medium, forexample, that designated 6N1-TGR-P4 to obtain callus or embryoids. Theembryoids are recognized visually by identification of embryonic-likestructures. At this stage, the embryoids are transferred progressivelythrough a series of regeneration media. In an illustrative embodiment,the shoot initiation medium comprises BAP (6-benzyl-amino-purine) andNAA (naphthalene acetic acid). Regeneration protocols for isolatedmicrospore cultures and anther cultures are similar.

VIII. ADDITIONAL TISSUE CULTURES AND REGENERATION

The present invention contemplates a corn plant regenerated from atissue culture of the inbred maize plant 90LDC2, or of a hybrid maizeplant produced by crossing 90LDC2. As is well known in the art, tissueculture of corn can be used for the in vitro regeneration of a cornplant. By way of example, a process of tissue culturing and regenerationof corn is described in European Patent Application 0 160 390, thedisclosure of which is incorporated by reference. Corn tissue cultureprocedures are also described in Green and Rhodes (1982) and Duncan etal. (1985). The study by Duncan et al. (1985) indicates that 97 percentof cultured plants produced calli capable of regenerating plants.Subsequent studies have shown that both inbreds and hybrids produced 91%regenerable calli that produced plants.

Other studies indicate that non-traditional tissues are capable ofproducing somatic embryogenesis and plant regeneration (Songstad et al.,1988; Rao et al., 1986; Conger et al, 1987; the disclosures of which areincorporated herein by reference). Regenerable cultures, including TypeI and Type II cultures, may be initiated from immature embryos asdescribed in, for example, PCT/WO95/06128, the disclosure of which isincorporated herein by reference in its entirety.

Briefly, by way of example, to regenerate a plant of this invention,cells are selected following growth in culture. Where employed, culturedcells are preferably grown either on solid supports or in the form ofliquid suspensions as set forth above. In either instance, nutrients areprovided to the cells in the form of media, and environmental conditionsare controlled. There are many types of tissue culture media comprisingamino acids, salts, sugars, hormones, and vitamins. Most of the mediaemployed to regenerate inbred and hybrid plants have some similarcomponents; the media differ in the composition and proportions of theiringredients depending on the particular application envisioned. Forexample, various cell types usually grow in more than one type of media,but exhibit different growth rates and different morphologies, dependingon the growth media. In some media, cells survive but do not divide.Various types of media suitable for culture of plant cells have beenpreviously described and discussed above.

An exemplary embodiment for culturing recipient corn cells in suspensioncultures includes using embryogenic cells in Type II (Armstrong andGreen, 1985; Gordon-Kamm et al., 1990) callus, selecting for small (10to 30 mm) isodiametric, cytoplasmically dense cells, growing the cellsin suspension cultures with hormone containing media, subculturing intoa progression of media to facilitate development of shoots and roots,and finally, hardening the plant and readying it metabolically forgrowth in soil.

Meristematic cells (i.e., plant cells capable of continual cell divisionand characterized by an undifferentiated cytological appearance,normally found at growing points or tissues in plants such as root tips,stem apices, lateral buds, etc.) can be cultured (PCT/WO96/04392;specifically incorporated herein by reference).

Embryogenic calli are produced essentially as described inPCT/WO95/06128. Specifically, inbred plants or plants from hybridsproduced from crossing an inbred of the present invention with anotherinbred are grown to flowering in a greenhouse. Explants from at leastone of the following F₁ tissues: the immature tassel tissue, intercalarymeristems and leaf bases, apical meristems, immature ears and immatureembryos are placed in an initiation medium which contain MS salts,supplemented with thiamine, agar, and sucrose. Cultures are incubated inthe dark at about 23° C. All culture manipulations and selections areperformed with the aid of a dissecting microscope.

After about 5 to 7 days, cellular outgrowths are observed from thesurface of the explants. After about 7 to 21 days, the outgrowths aresubcultured by placing them into fresh medium of the same composition.Some of the intact immature embryo explants are placed on fresh medium.Several subcultures later (after about 2 to 3 months) enough material ispresent from explants for subdivision of these embryogenic calli intotwo or more pieces.

Callus pieces from different explants are not mixed. Alter furthergrowth and subculture (about 6 months after embryogenic callusinitiation), there are usually between 1 and 100 pieces derivedultimately from each selected explant. During this time of cultureexpansion, a characteristic embryogenic culture morphology develops as aresult of careful selection at each subculture. Any organized structuresresembling roots or root primordia are discarded. Material known fromexperience to lack the capacity for sustained growth is also discarded(translucent, watery, embryogenic structures). Structures with a firmconsistency resembling at least in part the scutelum of the in vivoembryo are selected.

The callus is maintained on agar-solidified MS or N6-type media Apreferred hormone is 2,4-D. A second preferred hormone is dicamba.Visual selection of embryo-like structures is done to obtainsubcultures. Transfer of material other than that displaying embryogenicmorphology results in loss of the ability to recover whole plants fromthe callus.

Cell suspensions are prepared from the calli by selecting cellpopulations that appear homogeneous macroscopically. A portion of thefriable, rapidly growing embryogenic calli is inoculated into MS or N6Medium containing 2,4-D or dicamba. The calli in medium are incubated atabout 27° C. on a gyrotary shaker in the dark or in the presence of lowlight. The resultant suspension culture is transferred about once everythree to seven days, preferably every three to four days, by takingabout 5 to 10 ml of the culture and introducing this inoculum into freshmedium of the composition listed above (PCT/WO96/06128, specificallyincorporated herein by reference).

For regeneration, embryos which appear on the callus surface areselected and regenerated into whole plants by transferring theembryogenic structures into a sequence of solidified media which includedecreasing concentrations of 2,4-D or other auxins (PCT/WO96/06128,specifically incorporated herein by reference). Other hormones which canbe used in culture media include dicamba, NAA, ABA, BAP, and 2-NCA. Thereduction is relative to the concentration used in culture maintenancemedia Plantlets are regenerated from these embryos by transfer to ahormone-free medium, subsequently transferred to soil, and grown tomaturity.

Progeny are produced by taking pollen and selfing, backcrossing, orsibling regenerated plants by methods well known to those skilled in thearts. Seeds are collected from the regenerated plants.

IX. PROCESSES OF PREPARING CORN PLANTS AND THE CORN PLANTS PRODUCED BYSUCH CROSSES

The present invention also provides a process of preparing a novel cornplant and a corn plant produced by such a process. In accordance withsuch a process, a first parent corn plant is crossed with a secondparent corn plant wherein at least one of the first and second cornplants is the inbred corn plant 90LDC2. In one embodiment, a corn plantprepared by such a process is a first generation F₁ hybrid corn plantprepared by a process wherein both the first and second parent cornplants are inbred corn plants.

Corn plants (Zea mays L.) can be crossed by either natural or mechanicaltechniques. Natural pollination occurs in corn when wind blows pollenfrom the tassels to the silks that protrude from the tops of theincipient ears. Mechanical pollination can be effected either bycontrolling the types of pollen that can blow onto the silks or bypollinating by hand.

In a preferred embodiment, crossing comprises the steps of:

(a) planting in pollinating proximity seeds of a first and a secondparent corn plant, and preferably, seeds of a first inbred corn plantand a second, distinct inbred corn plant;

(b) cultivating or growing the seeds of the first and second parent cornplants into plants that bear flowers;

(c) emasculating flowers of either the first or second parent cornplant, i.e., treating the flowers so as to prevent pollen production, oralternatively, using as the female parent a male sterile plant, therebyproviding an emasculated parent corn plant;

(d) allowing natural cross-pollination to occur between the first andsecond parent corn plant;

(e) harvesting seeds produced on the emasculated parent corn plant; and,where desired,

(f) growing the harvested seed into a corn plant, or preferably, ahybrid corn plant.

Parental plants are planted in pollinating proximity to each other byplanting the parental plants in alternating rows, in blocks or in anyother convenient planting pattern. Plants of both parental parents arecultivated and allowed to grow until the time of flowering.Advantageously, during this growth stage, plants are in general treatedwith fertilizer and/or other agricultural chemicals as consideredappropriate by the grower.

At the time of flowering, in the event that plant 90LDC2 is employed asthe male parent, the tassels of the other parental plant are removedfrom all plants employed as the female parental plant. The detasselingcan be achieved manually but also can be done by machine, if desired.Alternatively, when the female parent corn plant comprises a cytoplasmicor nuclear gene conferring male sterility, detasseling may not berequired.

The plants are then allowed to continue to grow and naturalcross-pollination occurs as a result of the action of wind, which isnormal in the pollination of grasses, including corn. As a result of theemasculation of the female parent plant, all the pollen from the maleparent plant is available for pollination because tassels, and therebypollen bearing flowering parts, have been previously removed from allplants of the inbred plant being used as the female in thehybridization. Of course, during this hybridization procedure, theparental varieties are grown such that they are isolated from other cornfields to minimize or prevent any accidental contamination of pollenfrom foreign sources. These isolation techniques are well within theskill of those skilled in this art.

Both parental inbred plants of corn may be allowed to continue to growuntil maturity or the male rows may be destroyed after flowering iscomplete. Only the ears from the female inbred parental plants areharvested to obtain seeds of a novel F₁ hybrid. The novel F₁ hybrid seedproduced can then be planted in a subsequent growing season with thedesirable characteristics in terms of F₁ hybrid corn plants providingimproved grain yields and the other desirable characteristics disclosedherein, being achieved.

Alternatively, in another embodiment, both first and second parent cornplants can come from the same inbred corn plant, i.e., from the inbreddesignated 90LDC2. Thus, any corn plant produced using a process of thepresent invention and inbred corn plant 90LDC2, is contemplated by thisinvention. As used herein, crossing can mean selfing, backcrossing,crossing to another or the same inbred, crossing to populations, and thelike. All corn plants produced using the present inbred corn plant90LDC2 as a parent are within the scope of this invention.

The utility of the inbred plant 90LDC2 also extends to crosses withother species. Commonly, suitable species will be of the familyGraminaceae, and especially of the genera Zea, Tripsacum, Coix,Schlerachne, Polytoca, Chionachne, and Trilobachne, of the tribeMaydeae. Of these, Zea and Tripsacum, are most preferred. Potentiallysuitable for crosses with 90LDC2 can also be the various varieties ofgrain sorghum, Sorghum bicolor (L.) Moench.

A. F₁ HYBRID CORN PLANT AND SEED PRODUCTION

Any time an inbred corn plant 90LDC2 is crossed with another, different,corn inbred, a first generation (F₁) corn hybrid plant is produced. Thehybrid is produced regardless of the combining ability of the twoinbreds used. As such, an F₁ hybrid corn plant may be produced bycrossing 90LDC2 with any second inbred maize plant. Therefore, any F₁hybrid corn plant or corn seed which is produced with 90LDC2 as a parentis part of the present invention. An example of such an F₁ hybrid whichhas been produced with 90LDC2 as a parent is the hybrid 5000010.

The goal of the process of producing an F₁ hybrid is to manipulate thegenetic complement of corn to generate new combinations of genes whichinteract to yield new or improved traits (phenotypic characteristics). Aprocess of producing an F₁ hybrid typically begins with the productionof one or more inbred plants. Those plants are produced by repeatedcrossing of ancestrally related corn plants to try to combine certaingenes within the inbred plants.

Corn has a diploid phase which means two conditions of a gene (twoalleles) occupy each locus (position on a chromosome). If the allelesare the same at a locus, there is said to be homozygosity. If they aredifferent, there is said to be heterozygosity. In a completely inbredplant, all loci are homozygous. Because many loci when homozygous aredeleterious to the plant, in particular leading to reduced vigor, lesskernels, weak and/or poor growth, production of inbred plants is anunpredictable and arduous process. Under some conditions, heterozygousadvantage at some loci effectively bars perpetuation of homozygosity.

Inbreeding requires sophisticated manipulation by human breeders. Evenin the extremely unlikely event inbreeding rather than crossbreedingoccurred in natural corn, achievement of complete inbreeding cannot beexpected in nature due to well known deleterious effects of homozygosityand the large number of generations the plant would have to breed inisolation. The reason for the breeder to create inbred plants is to havea known reservoir of genes whose gametic transmission is at leastsomewhat predictable.

The development of inbred plants generally requires at least about 5 to7 generations of selfing. Inbred plants are then cross-bred in anattempt to develop improved F₁ hybrids. Hybrids are then screened andevaluated in small scale field trials. Typically, about 10 to 15phenotypic traits, selected for their potential commercial value, aremeasured. A selection index of the most commercially important traits isused to help evaluate hybrids. FACT, an acronym for Field AnalysisComparison Trial (strip trials), is an on-farm experimental testingprogram employed by DEKALB Genetics Corporation to perform the finalevaluation of the commercial potential of a product.

During the next several years, a progressive elimination of hybridsoccurs based on more detailed evaluation of their phenotype. Eventually,strip trials (FACT) are conducted to formally compare the experimentalhybrids being developed with other hybrids, some of which werepreviously developed and generally are commercially successful. That is,comparisons of experimental hybrids are made to competitive hybrids todetermine if there was any advantage to further development of theexperimental hybrids. Examples of such comparisons are presented inSection B, hereinbelow. After FACT testing is complete, determinationsmay be made whether commercial development should proceed for a givenhybrid.

When the inbred corn plant 90LDC2 is crossed with another inbred plantto yield a hybrid (such as the hybrid 5000010), the original inbred canserve as either the maternal or paternal plant. For many crosses, theoutcome is the same regardless of the assigned sex of the parentalplants.

However, there is often one of the parental plants that is preferred asthe maternal plant because of increased seed yield and productioncharacteristics. Some plants produce tighter ear husks leading to moreloss, for example due to rot. There can be delays in silk formationwhich deleteriously affect timing of the reproductive cycle for a pairof parental inbreds. Seed coat characteristics can be preferable in oneplant. Pollen can be shed better by one plant. Other variables can alsoaffect preferred sexual assignment of a particular cross. In the case ofthe instant invention, it was preferable to use 90LDC2 as the maleparent.

B. F₁ HYBRID COMPARISONS

As mentioned in Section A, hybrids are progressively eliminatedfollowing detailed evaluations of their phenotype, including formalcomparisons with other commercially successful hybrids. Strip trials areused to compare the phenotypes of hybrids grown in as many environmentsas possible. They are performed in many environments to assess overallperformance of the new hybrids and to select optimum growing conditions.Because the corn is grown in close proximity, environmental factors thataffect gene expression, such as moisture, temperature, sunlight, andpests, are minimized. For a decision to be made to commercialize ahybrid, it is not necessary that the hybrid be better than all otherhybrids. Rather, significant improvements must be shown in at least sometraits that would create improvements in some niches.

Examples of such comparative data are set forth hereinbelow in Table 5,which presents a comparison of performance data for the hybrid 5000010,a hybrid made with 90LDC2 as one parent, versus selected hybrids ofcommercial value (DK626 and DK642).

All the data in Table 5 represents results across years and locationsfor research and/or strip trials. The "NTEST" represents the number ofpaired observations in designated tests at locations around the UnitedStates.

                                      TABLE 5                                     __________________________________________________________________________    Comparative Data for 5000010                                                           SI YLD                                                                              MST                                                                              STL                                                                              RTL                                                                              DRP                                                                              FLSTD                                                                             SV ELSTD                                                                             PHT EHT BAR                                                                              SG TST    ESTR                 HYBRID NTEST % C BU PTS % % % % M RAT % M INCH INCH % RAT LBS FGDU          __________________________________________________________________________                                                               DAYS               5000010                                                                            R 326                                                                             106.2                                                                            168.7                                                                            19.8                                                                             4.2                                                                              3.4                                                                              0.6                                                                              100.5                                                                             3.4                                                                              101.7                                                                             98.0                                                                              48.3                                                                              1.3                                                                              6.1                                                                              56.2                                                                             1416                                                                              113.6                DK626  98.0 161.1 19.3 5.5 5.3 0.8 100.0 3.8 101.1 100.2 46.1 2.0 5.5                                                                  54.7 1422                                                                     113.0                DEV  8.2 7.6 0.5 -1.4 -1.9 -0.2 0.6 -0.4 0.6 -2.2 2.2 -0.7 0.6 1.6 -6                                                                  0.6                  SIG  ** ** ** ** *  ** **  ** **  ** **  **                                   5000010 F 143 94.0 149.4 19.3 7.6 3.7 1.8 102.4       57.6  112.9                                                                       DK626  92.9                                                                  149.7 18.7                                                                    10.9 3.9 2.2                                                                  100.8                                                                         56.2  112.0                                                                    DEV  1.1 -0.3                                                                0.6 -3.3 -0.2                                                                 -0.3 1.6                                                                      1.4  0.9                                                                       SIG    ** **                                                                  +        **                                                                  **                   5000010 R 317 106.4 169.2 19.9 4.2 3.4 0.6 100.5 3.4 101.7 98.3 48.7                                                                   1.3 6.1 56.2                                                                  1416 113.6                                                                     DK642  100.3                                                                 163.3 20.5 4.6                                                                1.5 0.5 100.1                                                                 3.3 99.4 97.1                                                                 40.8 3.2 4.8                                                                  55.1 1424                                                                     114.1                DEV  6.2 5.9 -0.6 -0.3 1.9 0.1 0.5 0.1 2.4 1.2 7.9 -1.9 1.3 1.1 -8 -0.5       SIG  ** ** **  **  **  ** +  ** * ** **  **                                   5000010 F 108 97.7 148.1 19.1 7.4 1.7 1.2 101.3       57.5  113.0                                                                       DK642  99.3                                                                  149.3 19.7 6.5                                                                0.4 0.9 100.4                                                                      56.2                                                                     113.6                DEV  -1.6 -1.2 -0.6 0.9 1.3 0.3 0.9       1.3  -0.6                           SIG    **           **  **                                                  __________________________________________________________________________     Signicance levels are indicated as: + = 70%, * = 5%, ** = 1%                  LEGEND ABBREVIATIONS:                                                         HYBD = Hybrid                                                                 NTEST = Research/FACT                                                         SI % C = Selection Index (percent of check)                                   YLD BU/A = Yield (bushels/acre)                                               MST PTS = Moisture                                                            STL % = Stalk Lodging (percent)                                               RTL % = Root Lodging (percent)                                                DRP % = Dropped Ears (percent)                                                FLSTD % M = Final Stand (percent of test mean)                                SV RAT = Seedling Vigor Rating                                                ELSTD % M = Early Stand (percent of test mean)                                PHI INCH = Plant Height (inches)                                              EHT INCH = Ear Height (inches)                                                BAR % = Barren Plants (percent)                                               SG RAT = Staygreen Rating                                                     TST LBS = Test Weight (pounds)                                                FGDU = GDUs to Shed                                                           ESTR DAYS = Estimated Relative Maturity (days)                           

As can be seen in Table 5, the hybrid 5000010 differs significantly in anumber of traits, when compared to the successful commercial hybridsDK626 and DK642.

C. PHYSICAL DESCRIPTION OF F₁ HYBRIDS

The present invention also provides F₁ hybrid corn plants derived fromthe corn plant 90LDC2. Physical characteristics of exemplary hybrids areset forth in Table 6, which concerns 5000010, a hybrid having 90LDC2 asone inbred parent. An explanation of terms used in Table 6 can be foundin the Definitions, set forth hereinabove.

                  TABLE 6                                                         ______________________________________                                        Morphological Traits for the 5000010 Phenotype                                  YEAR OF DATA: 1998                                                                CHARACTERISTIC VALUE                                                    ______________________________________                                        1. STALK                                                                        Diameter (width) cm. 2.5                                                      Anthocyanin Absent                                                            Nodes With Brace Roots 1.6                                                    Brace Root Color Faint                                                        Internode Direction Straight                                                  Internode Length cm. 19.1                                                     2. LEAF                                                                       Color Dark-Green                                                              Length cm. 98.6                                                               Width cm. 8.7                                                                 Sheath Pubescence Strong                                                      Marginal Waves Few                                                            Longitudinal Creases Few                                                      3. TASSEL                                                                     Length cm. 47.7                                                               Spike Length cm. 22.9                                                         Peduncle Length cm. 10.9                                                      Attitude Open                                                                 Branch Number 9.4                                                             Anther Color Tan                                                              Glume Color Green                                                             Glume Band Absent                                                             4. EAR                                                                        Silk Color Green-Yellow                                                       Number Per Stalk 1.0                                                          Position (attitude) Pendant                                                   Length cm. 18.6                                                               Shape Semi-Conical                                                            Diameter cm. 41.4                                                             Weight gm. 173.6                                                              Shank Length cm. 7.8                                                          Husk Bract Short                                                              Husk Cover cm. 5.0                                                            Husk Color Fresh Green                                                        Husk Color Dry Buff                                                           Cob Diameter cm. 24.1                                                         Cob Color Red                                                                 Shelling Percent 88.8                                                         5. KERNEL                                                                     Row Number 18.2                                                               Number Per Row 40.7                                                           Row Direction Curved                                                          Type Dent                                                                     Cap Color Yellow                                                              Side Color Orange                                                             Length (depth) mm. 11.5                                                       Width mm. 6.9                                                                 Thickness 3.9                                                                 Weight of 1000K gm. 227.5                                                     Endosperm Type Normal                                                         Endosperm Color Yellow                                                      ______________________________________                                         *These are typical values. Values mav vary due to environment. Other          values that are substantially equivalent are also within the scope of the     invention. Substantially equivalent refers to quantitative traits that        when compared do not show statistical dfferences of their means.         

X. GENETIC COMPLEMENTS

In another aspect, the present invention provides a genetic complementof a plant of this invention. In one embodiment, therefore, the presentinvention contemplates an inbred genetic complement of the inbred cornplant designated 90LDC2. In another embodiment, the present inventioncontemplates a hybrid genetic complement formed by the combination of ahaploid genetic complement from 90LDC2 and another haploid geneticcomplement. Means for determining a genetic complement are well-known inthe art.

As used herein, the phrase "genetic complement" means an aggregate ofnucleotide sequences, the expression of which sequences defines thephenotype of a corn plant or a cell or tissue of that plant. By way ofexample, a corn plant is genotyped to determine the array of theinherited markers it possesses. Markers are alleles at a single locus.They are preferably inherited in codominant fashion so that the presenceof both alleles at a diploid locus is readily detectable, and they arefree of environmental variation, i.e., their heritability is 1. Thisgenotyping is preferably performed on at least one generation of thedescendant plant for which the numerical value of the quantitative traitor traits of interest are also determined. The array of single locusgenotypes is expressed as a profile of marker alleles, two at eachlocus. The marker allelic composition of each locus can be eitherhomozygous or heterozygous. Homozygosity is a condition where bothalleles at a locus are characterized by the same nucleotide sequence.Heterozygosity refers to different conditions of the gene at a locus.Markers that are used for purposes of this invention include restrictionfragment length polymorphisms (RFLPs), simple sequence lengthpolymorphisms (SSLPs), amplified fragment length polymorphisms (AFLPs),and isozymes.

A plant genetic complement can be defined by genetic marker profilesthat can be considered "fingerprints" of a genetic complement. Forpurposes of this invention, markers are preferably distributed evenlythroughout the genome to increase the likelihood they will be near aquantitative trait loci (QTL) of interest (e.g., in tomatoes) (U.S. Pat.No. 5,385,835; Nienhuis et al., 1987). These profiles are partialprojections of a sample of genes. One of the uses of markers in generalis to exclude, or alternatively include, potential parents ascontributing to offspring.

Phenotypic traits characteristic of the expression of a geneticcomplement of this invention are distinguishable by electrophoreticseparation of DNA sequences cleaved by various restrictionendonucleases. Those traits (genetic markers) are termed RFLPs(restriction fragment length polymorphisms).

Restriction fragment length polymorphisms (RFLPs) are geneticdifferences detectable by DNA fragment lengths, typically revealed byagarose gel electrophoresis, after restriction endonuclease digestion ofDNA. There are large numbers of restriction endonucleases available,characterized by their nucleotide cleavage sites and their source, e.g.,EcoRI. Variations in RFLPs result from nucleotide base pair differenceswhich alter the cleavage sites of the restriction endonucleases,yielding different sized fragments.

Means for performing RFLP analyses are well known in the art. Therestriction fragment length polymorphism analyses reported herein wereconducted by Linkage Genetics (now PE AgGen, Inc., 2411 South 1070 West,Salt Lake City, Utah 84119). This service is available to the public ona contractual basis. Probes were prepared to the fragment sequences,these probes being complementary to the sequences thereby being capableof hybridizing to them under appropriate conditions well known to thoseskilled in the art. These probes were labeled with radioactive isotopesor fluorescent dyes for ease of detection. After the fragments wereseparated by size, they were identified by the probes. Hybridizationwith a unique cloned sequence permits the identification of a specificchromosomal region (locus). Because all alleles at a locus aredetectable, RFLPs are codominant alleles, thereby satisfying a criteriafor a genetic marker. They differ from some other types of markers,e.g., from isozymes, in that they reflect the primary DNA sequence, theyare not products of transcription or translation. Furthermore, differentRFLP genetic marker profiles result from different arrays of restrictionendonucleases.

The RFLP genetic marker profile of each of the parental inbreds andexemplary resultant hybrids were determined. Because an inbred isessentially homozygous at all relevant loci, an inbred should, in almostall cases, have only one allele at each locus. In contrast, a diploidgenetic marker profile of a hybrid should be the sum of those parents,e.g., if one inbred parent had the allele A at a particular locus, andthe other inbred parent had B, the hybrid is AB by inference. Subsequentgenerations of progeny produced by selection and breeding are expectedto be of genotype A, B, or AB for that locus position. When the F₁ plantis used to produce an inbred, the locus should be either A or B for thatposition. Surprisingly, it has been observed that in certain instances,novel RFLP genotypes arise during the breeding process. For example, agenotype of C is observed at a particular locus position from the crossof parental inbreds with A and B at that locus. Such a novel RFLPgenotype is observed for the 90LDC2, at least, for the RFLP markersMO306H and M1447H, as shown in Table 7. These novel RFLP markers furtherdefine the 90LDC2 inbred from the parental inbreds from which it wasderived. An RFLP genetic marker profile of 90LDC2 is presented in Table7.

                  TABLE 7                                                         ______________________________________                                        RFLP Profile of 90LDC2                                                          CHARACTERISTIC 90LDC2   LH210  MM501D 90LDC1                                ______________________________________                                        M0264H       M        F        M      M                                         M0306H A C F A                                                                M0445E A D A A                                                                M1120S C C B C                                                                M1234H F F B B                                                                M1236H A A B B                                                                M1238H G G E E                                                                M1401E B B B B                                                                M1406H A A A A                                                                M1447H E A A A                                                                M1B725E B H B H                                                               M2239H C D C C                                                                M2297H C C C C                                                                M2298E F F A A                                                                M2402H E --  E E                                                              M3212S A C A A                                                                M3247E B B D B                                                                M3257S A -- A --                                                              M3296H C C A --                                                               M3446S C C C C                                                                M3457E D E D E                                                                M3486H D -- B B                                                               M4396H C C B B                                                                M4444H A A A A                                                                M4451H A A -- --                                                              M4UMC19H A A C C                                                              M4UMC31S D D B D                                                              M5213S A A A A                                                                M5288S A -- A A                                                               M5295E C C C C                                                                M5408H A A A A                                                                M5409H C C C C                                                                M5UMC95H A A C --                                                             M6223E D D C C                                                                M6252H A A A A                                                                M6280H B B I B                                                                M6373E E E A J                                                                M7263E B B C B                                                                M7391H A A A A                                                                M7392S B B B B                                                                M7455H B B B B                                                                M8107S D D F F                                                                M8110S C A C C                                                                M8114E C E D D                                                                M8268H A A C C                                                                M8585H B E B B                                                                M8UMC48E C D C C                                                              M9209E A A A A                                                                M9B713S C C B B                                                               M2UMC34H B -- B --                                                            M6UMC85H C A C --                                                             M9UMC94H A E A --                                                             M3UM121X D D D D                                                              M0UMC130 A A -- C                                                           ______________________________________                                         *Probes used to detect RFLPs are from Linkage Genetics, 1515 West 2200        South, Suite C, Salt Lake City, Utah 84119.                              

Another aspect of this invention is a plant genetic complementcharacterized by a genetic isozyme typing profile. Isozymes are forms ofproteins that are distinguishable, for example, on starch gelelectrophoresis, usually by charge and/or molecular weight. Thetechniques and nomenclature for isozyme analysis are described in,Stuber et al. (1988), which is incorporated by reference.

A standard set of loci can be used as a reference set. Comparativeanalysis of these loci is used to compare the purity of hybrid seeds, toassess the increased variability in hybrids compared to inbreds, and todetermine the identity of seeds, plants, and plant parts. In thisrespect, an isozyme reference set can be used to develop genotypic"fingerprints."

Table 8 lists the identifying numbers of the alleles at isozyme locitypes, and represents the exemplary genetic isozyme typing profile for90LDC2.

                  TABLE 8                                                         ______________________________________                                        Isozyme Profile of 90LDC2                                                            ISOZYME ALLELE                                                         L0CI   90LDC2    LH210    MM501D     90LDC1                                   ______________________________________                                        Acph1  2         2        4(5k),2/4(1k)*                                                                           4                                          Adh1 4 4 4 4                                                                  Cat3 9 9 9 9                                                                  Got3 NS 4 NS 4                                                                Got2 4 4 4 4                                                                  Got1 4 4 4 4                                                                  Idh1 4 4 4 4                                                                  Idh2 4 4 6(5k),4/6(1k)* 4                                                     Mdh1 6 6 6 6                                                                  Mdh2 6** 6** 6(5k)**,3/6(1k)* 6**                                             Mdh3 16 16 16 16                                                              Mdh4 12 12 12 12                                                              Mdh5 12 12 12 12                                                              Pgm1 9 9 9 9                                                                  Pgm2 4 4 4 4                                                                  6Pgd1 3.8 3.8 2(5k),2/3.8(1k)* 2                                              6Pgd2 n n 5 5                                                                 Phi1 4 4 4(5k),4/5(1k)* 4                                                   ______________________________________                                         NS-enzyme system was not scorable.                                            **allele is probably a 6, but a null cannot be ruled out                      *This one kernel could be an offtype: for the same kernel, Acph1 = 2/4;       Mdh2 = 3; 6Pgd1 = 2/3.8;Phi = 4/5                                        

The present invention contemplates a hybrid genetic complement formed bythe combination of a haploid genetic complement of the corn plant 90LDC2with a haploid genetic complement of a second corn plant. Means forcombining a haploid genetic complement from the foregoing inbred withanother haploid genetic complement can be any method hereinbefore forproducing a hybrid plant from 90LDC2. It is also contemplated that ahybrid genetic complement can be prepared using in vitro regeneration ofa tissue culture of a hybrid plant of this invention.

A hybrid genetic complement contained in the seed of a hybrid derivedfrom 90LDC2 is a further aspect of this invention. Exemplary hybridgenetic complements are the genetic complements of the hybrid 5000010.

Table 9 shows the identifying numbers of the alleles for the hybrid5000010, which are exemplary RFLP genetic marker profiles for hybridsderived from the inbred of the present invention. Table 9 concerns5000010, which has 90LDC2 as one inbred parent.

                  TABLE 9                                                         ______________________________________                                        RFLP Profile for 5000010                                                            Probe/Enzyme Combination                                                                      Allelic Pair                                            ______________________________________                                        M0264H            GM                                                            M0306H AA                                                                     M1120S BC                                                                     M1234H EF                                                                     M1236H AA                                                                     M1238H FG                                                                     M1401E AB                                                                     M1406H AA                                                                     M1447H BE                                                                     M1B725E BB                                                                    M2239H CG                                                                     M2297H AC                                                                     M2298E BF                                                                     M2402H EE                                                                     M3212S AB                                                                     M3247E BD                                                                     M3257S AC                                                                     M3296H CC                                                                     M3446S CF                                                                     M3457E DF                                                                     M3486H BD                                                                     M4396H AC                                                                     M4444H AB                                                                     M4UMC19H AB                                                                   M4UMC31S BD                                                                   M5213S AA                                                                     M5288S AA                                                                     M5295E CD                                                                     M5409H CC                                                                     M5UMC95H AA                                                                   M6223E CD                                                                     M6252H AF                                                                     M6280H BB                                                                     M6373E EE                                                                     M7263E BC                                                                     M7391H AA                                                                     M7392S BB                                                                     M7455H BC                                                                     M8107S DF                                                                     M8110S CC                                                                     M8114E BC                                                                     M8268H AB                                                                     M8585H AB                                                                     M8UMC48E AC                                                                   M9209E AA                                                                     M9B713S AC                                                                    M2UMC34H BE                                                                   M6UMC85H AC                                                                   M9UMC94H AB                                                                   M3UM121X CD                                                                   M0UMC130 AH                                                                 ______________________________________                                         *Probes used to detect RFLPs are from Linkage Genetics, 1515 West 2200        South, Suite C, Salt Lake City, Utah 84119.                              

The exemplary hybrid genetic complements of hybrid 5000010 may also beassessed by genetic isozyme typing profiles using a standard set of locias a reference set, using, e.g., the same, or a different, set of locito those described above. Table 10 lists the identifying numbers of thealleles at isozyme loci types and presents the exemplary genetic isozymetyping profile for the hybrid 5000010, which is an exemplary hybridderived from the inbred of the present invention. Table 10 concerns5000010, which has 90LDC2 as one inbred parent.

                  TABLE 10                                                        ______________________________________                                        Isozyme Genotype for Hybrid 5000010                                                    Loci    Isozyme Allele                                               ______________________________________                                               Acph1 2                                                                  Adh1 4                                                                        Cat3 9                                                                        Got3 NS                                                                       Got2 4                                                                        Got1 4                                                                        Idh1 4                                                                        Idh2 4                                                                        Mdh1 6                                                                        Mdh2 3.5/6                                                                    Mdh3 16                                                                       Mdh4 12                                                                       Mdh5 12                                                                       Pgm1 9                                                                        Pgm2 4                                                                        6-Pgd1 2/3.8                                                                  6-Pgd2 n/5                                                                    Phi1 4                                                                      ______________________________________                                         NS-one or more alleles were not scorable                                 

All of the compositions and methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the compositions and methods of this invention havebeen described in terms of the foregoing illustrative embodiments, itwill be apparent to those of skill in the art that variations, changes,modifications, and alterations may be applied to the composition,methods, and in the steps or in the sequence of steps of the methodsdescribed herein, without departing from the true concept, spirit, andscope of the invention. More specifically, it will be apparent thatcertain agents that are both chemically and physiologically related maybe substituted for the agents described herein while the same or similarresults would be achieved. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope, and concept of the invention as defined by theappended claims.

REFERENCES

The following references, to the extent that they provide exemplaryprocedural or other details supplementary to those set forth herein, arespecifically incorporated herein by reference.

Anderson, W. P., Weed Science Principles, West Publishing Company, 1983.

Armstrong and Green, "Establishment and maintenance of friable,embryogenic maize callus and the involvement of L-proline," Planta,164:207-214, 1985.

Conger, Novak, Afza, Erdelsky, "Somatic Embryogenesis from Cultured LeafSegments of Zea Mays," Plant Cell Reports, 6:345-347, 1987.

Duncan et al., "The Production of Callus Capable of Plant Regenerationfrom Immature Embryos of Numerous Zea Mays Genotypes," Planta,165:322-332, 1985.

Fehr, "Theory and Technique," In: Principles of Cultivar Development, 1:360-376, 1987.

Gaillard et al., "Optimization of Maize Microspore Isolation and CultureCondition for Reliable Plant Regeneration," Plant Cell Reports,10(2):55, 1991.

Gordon-Kamm, Spencer, Mangano, Adams, Daines, Start, O'Brien, Chambers,Adams, Jr., Willetts, Rice, Mackey, Krueger, Kausch, Lemaux,"Transformation of Maize Cells and Regeneration of Fertile TransgenicPlants," The Plant Cell, 2:603-618, 1990.

Green and Rhodes, "Plant Regeneration in Tissue Cultures of Maize:Callus Formation from Stem Protoplasts of Corn (Zea Mays L.)," In: Maizefor Biological Research, 367-372, 1982.

Jensen, "Chromosome Doubling Techniques in Haploids," Haploids andHigher Plants--Advances and Potentials, Proceedings of the FirstInternational Symposium, 1974.

Nienhuis et al., "Restriction Fragment Length Polymorphism Analysis ofLoci Associated with Insect Resistance in Tomato," Crop Science,27(4):797-803, 1987.

Omirulleh et al., "Activity of a chimeric promoter with the doubled CAMV35S enhancer element in protoplast-derived cells and transgenic plantsin maize," Plant Mol. Biol., 21(3):415-428, 1993.

Pace et al., "Anther Culture of Maize and the Visualization ofEmbryogenic Microspores by Fluorescent Microscopy," Theoretical andApplied Genetics, 73:863-869, 1987.

Poehlman et al., "Breeding Field Crops," 4th Ed., Iowa State UniversityPress, Ames, Iowa, pp 132-155 and 321-344.

Rao et al., "Somatic Embryogenesis in Glume Callus Cultures," MaizeGenetics Cooperation Newsletter, 60, 1986.

Songstad et al., "Effect of 1-Aminocyclopropate-1-Carboxylic Acid,Silver Nitrate, and Norbornadiene on Plant Regeneration from MaizeCallus Cultures," Plant Cell Reports, 7:262-265, 1988.

Sprague and Dudley (eds.), "Corn and Corn Improvement," 3rd Ed., CropScience of America, Inc., and Soil Science of America, Inc., MadisonWis. pp 881-883 and pp 901-918, 1988.

Stuber et al., "Techniques and scoring procedures for starch gelelectrophoresis of enzymes of maize C. Zea mays, L.," Tech. Bull., 286,1988.

Wan et al., "Efficient Production of Doubled Haploid Plants ThroughColchicine Treatment of Anther-Derived Maize Callus," Theoretical andApplied Genetics, 77:889-892, 1989.

Williams et al., "Oligonucleotide Primers of Arbitrary Sequence AmplifyDNA Polymorphisms which Are Useful as Genetic Markers," Nucleic AcidsRes., 18:6531-6535, 1990.

What is claimed is:
 1. Inbred corn seed of the corn plant 90LDC2, asample of said seed having been deposited under accession numberPTA-305.
 2. The inbred corn seed of claim 1, further defined as anessentially homogeneous population of inbred corn seed.
 3. The inbredcorn seed of claim 1, further defined as essentially free from hybridseed.
 4. An inbred corn plant produced by growing the seed of the inbredcorn plant 90LDC2, a sample of said seed having been deposited underaccession number PTA-305.
 5. Pollen of the plant of claim
 4. 6. An ovuleof the plant of claim
 4. 7. An essentially homogeneous population ofcorn plants produced by growing the seed of the inbred corn plant90LDC2, a sample of said seed having been deposited under accessionnumber PTA-305.
 8. A corn plant capable of expressing all thephysiological and morphological characteristics of the inbred corn plant90LDC2, a sample of the seed of said inbred corn plant 90LDC2 havingbeen deposited under accession number PTA-305.
 9. The corn plant ofclaim 8, further comprising a factor conferring male sterility.
 10. Atissue culture of regenerable cells of inbred corn plant 90LDC2, whereinthe tissue regenerates plants capable of expressing all thephysiological and morphological characteristics of the inbred corn plant90LDC2, a sample of the seed of said inbred corn plant 90LDC2 havingbeen deposited under accession number PTA-305.
 11. The tissue culture ofclaim 10, wherein the regenerable cells comprise cells derived fromembryos, immature embryos, meristematic cells, immature tassels,microspores, pollen, leaves, anthers, roots, root tips, silk, flowers,kernels, ears, cobs, husks, or stalks.
 12. The tissue culture of claim11, wherein the regenerable cells comprise protoplasts or callus.
 13. Acorn plant regenerated from the tissue culture of claim 10, wherein saidcorn plant is capable of expressing all of the physiological andmorphological characteristics of the inbred corn plant 90LDC2, a sampleof the seed of said inbred corn plant 90LDC2 having been deposited underaccession number PTA-305.
 14. An inbred corn plant cell of the cornplant of claim 8, said cell comprising:(a) an RFLP genetic markerprofile in accordance with the profile shown in Table 7; or (b) agenetic isozyme typing profile in accordance with the profile shown inTable
 8. 15. The inbred corn plant cell of claim 14, comprising an RFLPgenetic marker profile in accordance with the profile shown in Table 7.16. The inbred corn plant cell of claim 14, comprising a genetic isozymetyping profile in accordance with the profile shown in Table
 8. 17. Theinbred corn plant cell of claim 14, comprising an RFLP genetic markerprofile and a genetic isozyme typing profile in accordance with theprofiles shown in Table 7 and Table
 8. 18. A corn seed comprising theinbred corn plant cell of claim
 14. 19. A tissue culture comprising theinbred corn plant cell of claim
 14. 20. The inbred corn plant of claim8, comprising:(a) an RFLP genetic marker profile in accordance with theprofile shown in Table 7; or (b) a genetic isozyme typing profile inaccordance with the profile shown in Table
 8. 21. The inbred corn plantof claim 20, comprising an RFLP genetic marker profile in accordancewith the profile shown in Table
 7. 22. The inbred corn plant of claim20, comprising a genetic isozyme typing profile in accordance with theprofile shown in Table
 8. 23. The inbred corn plant of claim 20,comprising an RFLP genetic marker profile and a genetic isozyme typingprofile in accordance with the profiles shown in Table 7 and Table 8.24. A process of producing corn seed, comprising crossing a first parentcorn plant with a second parent corn plant, wherein said first or secondcorn plant is the inbred corn plant 90LDC2, a sample of the seed of saidinbred corn plant 90LDC2 having been deposited under accession numberPTA-305, wherein seed is allowed to form.
 25. The process of claim 24,further defined as a process of preparing hybrid corn seed, comprisingcrossing a first inbred corn plant with a second, distinct inbred cornplant, wherein said first or second inbred corn plant is the inbred cornplant 90LDC2, a sample of the seed of said inbred corn plant 90LDC2having been deposited under accession number PTA-305.
 26. The process ofclaim 25, wherein crossing comprises the steps of:(a) planting inpollinating proximity seeds of said first and second inbred corn plants;(b) cultivating the seeds of said first and second inbred corn plantsinto plants that bear flowers; (c) emasculating the male flowers of saidfirst or second inbred corn plant to produce an emasculated corn plant;(d) allowing cross-pollination to occur between said first and secondinbred corn plants; and (e) harvesting seeds produced on saidemasculated corn plant.
 27. The process of claim 26, further comprisinggrowing said harvested seed to produce a hybrid corn plant.
 28. Hybridcorn seed produced by the process of claim
 26. 29. A hybrid corn plantproduced by the process of claim
 27. 30. The hybrid corn plant of claim29, wherein the plant is a first generation (F₁) hybrid corn plant. 31.The corn plant of claim 4, further comprising a single locus conversion.32. The corn plant of claim 31, wherein the single locus was stablyinserted into a corn genome by transformation.
 33. The corn plant ofclaim 31, wherein the locus is a dominant allele.
 34. The corn plant ofclaim 31, wherein the locus is a recessive allele.
 35. The corn plant ofclaim 31, wherein the locus confers herbicide resistance.
 36. The cornplant of claim 31, wherein the locus confers insect resistance.
 37. Thecorn plant of claim 31, wherein the locus confers resistance tobacterial, fungal, nematode or viral disease.
 38. The corn plant ofclaim 31, wherein the locus confers yield enhancement.
 39. The cornplant of claim 31, wherein the locus confers waxy starch.
 40. The cornplant of claim 31, wherein the locus confers improved nutritionalquality.
 41. The corn plant of claim 31, wherein the locus confersenhanced yield stability.
 42. The corn plant of claim 31, wherein thelocus confers male sterility.
 43. The corn plant of claim 31, whereinthe locus comprises a male fertility restorer gene.